Signaling color values for 3D lookup table for color gamut scalability in multi-layer video coding

ABSTRACT

Techniques are described for signaling information used to generate three-dimensional (3D) color lookup tables for color gamut scalability in multi-layer video coding. A lower layer of video data may include color data in a first color gamut and a higher layer of the video data may include color data in a second color gamut. To generate inter-layer reference pictures, a video encoder and/or video decoder performs color prediction to convert the color data of a reference picture in the first color gamut to the second color gamut. The video coder may perform color prediction using a 3D lookup table. According to the techniques, a video encoder may encode partition information and/or color values of a 3D lookup table generated for color gamut scalability. A video decoder may decode the partition information and/or color values to generate the 3D lookup table in order to perform color gamut scalability.

RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.14/572,002, filed Dec. 16, 2014, which claims the benefit of U.S.Provisional Application No. 61/917,228, filed Dec. 17, 2013, and U.S.Provisional Application No. 62/005,845, filed May 30, 2014, the contentsof each of which are hereby incorporated by reference in their entirety.

TECHNICAL FIELD

This disclosure relates to video coding.

BACKGROUND

Digital video capabilities can be incorporated into a wide range ofdevices, including digital televisions, digital direct broadcastsystems, wireless broadcast systems, personal digital assistants (PDAs),laptop or desktop computers, tablet computers, e-book readers, digitalcameras, digital recording devices, digital media players, video gamingdevices, video game consoles, cellular or satellite radio telephones,so-called “smart phones,” video teleconferencing devices, videostreaming devices, and the like. Digital video devices implement videocoding techniques, such as those described in the standards defined byMPEG-2, MPEG-4, ITU-T H.263, ITU-T H.264/MPEG-4, Part 10, Advanced VideoCoding (AVC), the High Efficiency Video Coding (HEVC) standard, andextensions of such standards. The video devices may transmit, receive,encode, decode, and/or store digital video information more efficientlyby implementing such video coding techniques.

Video coding techniques include spatial (intra-picture) predictionand/or temporal (inter-picture) prediction to reduce or removeredundancy inherent in video sequences. For block-based video coding, avideo slice (e.g., a video frame or a portion of a video frame) may bepartitioned into video blocks, which may also be referred to astreeblocks, coding units (CUs) and/or coding nodes. Video blocks in anintra-coded (I) slice of a picture are encoded using spatial predictionwith respect to reference samples in neighboring blocks in the samepicture. Video blocks in an inter-coded (P or B) slice of a picture mayuse spatial prediction with respect to reference samples in neighboringblocks in the same picture or temporal prediction with respect toreference samples in other reference pictures. Pictures may be referredto as frames, and reference pictures may be referred to as referenceframes.

Spatial or temporal prediction results in a predictive block for a blockto be coded. Residual data represents pixel differences between theoriginal block to be coded and the predictive block. An inter-codedblock is encoded according to a motion vector that points to a block ofreference samples forming the predictive block, and the residual dataindicating the difference between the coded block and the predictiveblock. An intra-coded block is encoded according to an intra-coding modeand the residual data. For further compression, the residual data may betransformed from the pixel domain to a transform domain, resulting inresidual transform coefficients, which then may be quantized. Thequantized transform coefficients, initially arranged in atwo-dimensional array, may be scanned in order to produce aone-dimensional vector of transform coefficients, and entropy coding maybe applied to achieve even more compression.

SUMMARY

In general, this disclosure describes techniques for signalinginformation used to generate three-dimensional (3D) color lookup tablesfor color gamut scalability in multi-layer video coding. Colorprediction techniques for color gamut scalability may be used by videoencoders and/or video decoders to generate inter-layer referencepictures when a color gamut for a lower layer of video data is differentthan a color gamut for a higher layer of the video data. For example, avideo encoder and/or video decoder may first perform color predictionusing a 3D lookup table for color gamut scalability to convert the colordata of a reference picture for the lower layer to the color gamut forthe higher layer, and then generate inter-layer reference pictures basedon the converted color data. According to the techniques described inthis disclosure, a video encoder may encode partition information and/orcolor values of a 3D lookup table generated for color gamut scalability.A video decoder may decode the partition information and/or color valuesto generate the 3D lookup table in order to perform color gamutscalability.

In one example, this disclosure is directed toward a method of decodingvideo data, the method comprising determining a base partition value fora three-dimensional (3D) lookup table for color gamut scalability;determining a luma partition value for a luma component of the 3D lookuptable; and generating the 3D lookup table with coarser partitioning forchroma components and finer partitioning for the luma component,including partitioning each of the luma component, a first chromacomponent and a second chroma component of the 3D lookup table into afirst number of octants based on the base partition value, andpartitioning each of the first number of octants of the luma componentinto a second number of octants based on the luma partition value.

In another example, this disclosure is directed toward a method ofencoding video data, the method comprising generating athree-dimensional (3D) lookup table for color gamut scalability withcoarser partitioning for chroma components and finer partitioning for aluma component, including partitioning each of the luma component, afirst chroma component and a second chroma component of the 3D lookuptable into a first number of octants based on a base partition value forthe 3D lookup table, and partitioning each of the first number ofoctants of the luma component into a second number of octants based on aluma partition value for the luma component of the 3D lookup table.

In a further example, this disclosure is directed toward a videodecoding device comprising a memory configured to store video data; andone or more processors in communication with the memory. The one or moreprocessors are configured to determine a base partition value for athree-dimensional (3D) lookup table for color gamut scalability of thevideo data, determine a luma partition value for a luma component of the3D lookup table, and generate the 3D lookup table with coarserpartitioning for chroma components and finer partitioning for the lumacomponent, the one or more processors configured to partition each ofthe luma component, a first chroma component and a second chromacomponent of the 3D lookup table into a first number of octants based onthe base partition value, and partition each of the first number ofoctants of the luma component into a second number of octants based onthe luma partition value.

In another example, this disclosure is directed toward a video encodingdevice comprising a memory configured to store video data; and one ormore processors in communication with the memory. The one or moreprocessors are configured to generate a three-dimensional (3D) lookuptable for color gamut scalability of the video data with coarserpartitioning for chroma components and finer partitioning for a lumacomponent, the one or more processors configured to partition each ofthe luma component, a first chroma component and a second chromacomponent of the 3D lookup table into a first number of octants based ona base partition value, and partition each of the first number ofoctants of the luma component into a second number of octants based on aluma partition value for the luma component of the 3D lookup table.

In an additional example, this disclosure is directed toward a videodecoding device comprising means for determining a base partition valuefor a three-dimensional (3D) lookup table for color gamut scalability;means for determining a luma partition value for a luma component of the3D lookup table; and means for generating the 3D lookup table withcoarser partitioning for chroma components and finer partitioning forthe luma component, including means for partitioning each of the lumacomponent, a first chroma component and a second chroma component of the3D lookup table into a first number of octants based on the basepartition value, and means for partitioning each of the first number ofoctants of the luma component into a second number of octants based onthe luma partition value.

In a further example, this disclosure is directed toward acomputer-readable storage medium storing instructions for decoding videodata that, when executed, cause one or more processors to determine abase partition value for a three-dimensional (3D) lookup table for colorgamut scalability; determine a luma partition value for a luma componentof the 3D lookup table; and generate the 3D lookup table with coarserpartitioning for chroma components and finer partitioning for the lumacomponent, the instructions cause the one or more processors topartition each of the luma component, a first chroma component and asecond chroma component of the 3D lookup table into a first number ofoctants based on the base partition value, and partition each of thefirst number of octants of the luma component into a second number ofoctants based on the luma partition value.

In another example, this disclosure is directed toward a method ofdecoding video data, the method comprising determining a number ofoctants for each of three color components of a three-dimensional (3D)lookup table for color gamut scalability; for each of the octants foreach of the color components, decoding color mapping coefficients for alinear color mapping function of color values in the 3D lookup tableused to convert color data in a first color gamut for a lower layer ofthe video data to a second color gamut for a higher layer of the videodata; and generating the 3D lookup table based on the number of octantsfor each of the color components and color values associated with thecolor mapping coefficients for each of the octants.

In a further example, this disclosure is directed toward a method ofencoding video data, the method comprising generating athree-dimensional (3D) lookup table for color gamut scalability based ona number of octants for each of three color components and color valuesfor each of the octants; and for each of the octants for each of thecolor components, encoding color mapping coefficients for a linear colormapping function of the color values in the 3D lookup table used toconvert color data in a first color gamut for a lower layer of the videodata to a second color gamut for a higher layer of the video data.

In an additional example, this disclosure is directed toward a videodecoding device comprising a memory configured to store video data; andone or more processors in communication with the memory. The one or moreprocessors are configured to determine a number of octants for each ofthree color components of a three-dimensional (3D) lookup table forcolor gamut scalability of the video data, for each of the octants foreach of the color components, decode color mapping coefficients for alinear color mapping function of color values in the 3D lookup tableused to convert color data in a first color gamut for a lower layer ofthe video data to a second color gamut for a higher layer of the videodata, and generate the 3D lookup table based on the number of octantsfor each of the color components and color values associated with thecolor mapping coefficients for each of the octants.

In a further example, this disclosure is directed toward a videoencoding device comprising a memory configured to store video data; andone or more processors in communication with the memory. The one or moreprocessors are configured to generate a three-dimensional (3D) lookuptable for color gamut scalability of the video data based on a number ofoctants for each of three color components and color values for each ofthe octants; and for each of the octants for each of the colorcomponents, encode color mapping coefficients for a linear color mappingfunction of the color values in the 3D lookup table used to convertcolor data in a first color gamut for a lower layer of the video data toa second color gamut for a higher layer of the video data.

In another example, this disclosure is directed toward a video decodingdevice comprising means for determining a number of octants for each ofthree color components of a three-dimensional (3D) lookup table forcolor gamut scalability; means for decoding, for each of the octants foreach of the color components, color mapping coefficients for a linearcolor mapping function of color values in the 3D lookup table used toconvert color data in a first color gamut for a lower layer of the videodata to a second color gamut for a higher layer of the video data; andmeans for generating the 3D lookup table based on the number of octantsfor each of the color components and color values associated with thecolor mapping coefficients for each of the octants.

In an additional example, this disclosure is directed toward acomputer-readable storage medium storing instructions for decoding videodata that, when executed, cause one or more processors to determine anumber of octants for each of three color components of athree-dimensional (3D) lookup table for color gamut scalability; foreach of the octants for each of the color components, decode colormapping coefficients for a linear color mapping function of color valuesin the 3D lookup table used to convert color data in a first color gamutfor a lower layer of the video data to a second color gamut for a higherlayer of the video data; and generate the 3D lookup table based on thenumber of octants for each of the color components and color valuesassociated with the color mapping coefficients for each of the octants.

The details of one or more examples are set forth in the accompanyingdrawings and the description below. Other features, objects, andadvantages will be apparent from the description and drawings, and fromthe claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram illustrating an example video encoding anddecoding system that may utilize techniques for 3D lookup table basedcolor gamut scalability.

FIG. 2 is a conceptual illustration showing an example of scalability inthree different dimensions.

FIG. 3 is a conceptual illustration showing an example structure of ascalable video coding bitstream.

FIG. 4 is a conceptual illustration showing example scalable videocoding access units in bitstream order.

FIG. 5 is a block diagram illustrating an example scalable video codingextension to HEVC (SHVC) encoder.

FIG. 6 is a graph illustrating an example color gamut of a sample videosequence.

FIG. 7 is a block diagram illustrating conversion from high definition(HD) color gamut BT.709 to ultra-high definition (UHD) color gamutBT.2020.

FIG. 8 is a block diagram illustrating a color gamut scalable coderincluding a color prediction processing unit that may generate aninter-layer reference picture when a base layer color gamut and anenhancement layer color gamut are different.

FIGS. 9(a) and 9(b) are conceptual illustrations showing an example 3Dlookup table for color gamut scalability.

FIG. 10 is a conceptual illustration showing tri-linear interpolationwith a 3D lookup table for color gamut scalability.

FIG. 11 is a conceptual illustration showing tetrahedral interpolationwith a 3D lookup table for color gamut scalability.

FIG. 12 is a conceptual illustration showing six examples oftetrahedrons used to encompass a point P of a 3D lookup table to beinterpolated using tetrahedral interpolation.

FIG. 13 is a conceptual illustration showing an example 3D lookup tablewith an independently partitioned luma component and jointly partitionedchroma components.

FIG. 14 is a block diagram illustrating an example of a video encoderthat may implement techniques for using 3D lookup table based colorgamut scalability in multi-layer video coding.

FIG. 15 is a block diagram illustrating an example of a video decoderthat may implement techniques for using 3D lookup table based colorgamut scalability in multi-layer video coding.

FIG. 16 is a flowchart illustrating an example operation of encodingpartition information for at least one of the color components of a 3Dlookup table.

FIG. 17 is a flowchart illustrating an example operation of decodingpartition information for at least one of the color components of a 3Dlookup table.

FIG. 18 is a flowchart illustrating an example operation of encodingcolor values for each of the octants for each of the color components ofa 3D lookup table.

FIG. 19 is a flowchart illustrating an example operation of decodingcolor values for each of the octants for each of the color components ofa 3D lookup table.

DETAILED DESCRIPTION

This disclosure describes techniques for three-dimensional (3D) colorprediction for color gamut scalability in multi-layer video coding. Themulti-layer video coding may be in accordance the High Efficiency VideoCoding (HEVC) standard, including any of a scalable video codingextension, a multiview video coding extension, a 3D video coding (i.e.,multiview video coding plus depth) extension, or other multi-layer videocoding extensions to HEVC. The techniques may be used by video encodersand/or video decoders to generate inter-layer reference pictures when acolor gamut for a lower layer of video data is different than a colorgamut for a higher layer of the video data. In some examples, thetechniques may also be used when a bit depth of the lower layer of videodata is different than a bit depth for the higher layer of the videodata.

A color gamut comprises a complete range of colors that can bereproduced for an image, e.g., in a picture, slice, block or layer ofvideo data. Conventionally, in multi-layer video coding, a lower layerof video data (e.g., a base layer) and a higher layer of the video data(e.g., an enhancement layer) include color data in the same color gamut,e.g., high definition (HD) color gamut BT.709. In this case, a videoencoder and/or video decoder may generate inter-layer reference picturesfor the higher layer of the video data as up-sampled versions ofco-located reference pictures for the lower layer of the video data.

In some examples, however, a lower layer of video data may include colordata in a first color gamut, e.g., BT.709, and a higher layer of thevideo data may include color data in a different, second color gamut,e.g., ultra-high definition (UHD) color gamut BT.2020. In this example,in order to generate inter-layer reference pictures for the higher layerof the video data, a video encoder and/or video decoder must firstperform color prediction to convert the color data of a referencepicture in the first color gamut for the lower layer of the video datato the second color gamut for the higher layer of the video data.

The video encoder and/or video decoder may perform color predictionusing a 3D lookup table for color gamut scalability. In some examples, aseparate 3D lookup table may be generated for each of the colorcomponents, i.e., a luma (Y) component, a first chroma (U) component anda second chroma (V) component. Each of the 3D lookup tables includes aluma (Y) dimension, a first chroma (U) dimension and a second chroma (V)dimension, and is indexed using the three independent color components(Y, U, V).

Conventionally, the 3D lookup tables are always symmetric such that the3D lookup tables have a same size for the luma component, the firstchroma component and the second chroma component. In addition,conventionally, the 3D lookup tables are always balanced such that asize of each dimension of the 3D lookup tables is always the same. Thismay result in large table sizes with high computational complexity andhigh signaling costs. For example, table sizes may be up to 9×9×9 or17×17×17.

In U.S. patent application Ser. No. 14/512,177 , filed Oct. 10, 2014,techniques are described that enable a video encoder and/or videodecoder to generate an asymmetric and/or unbalanced 3D lookup table suchthat the 3D lookup table has a size that is different for the lumacomponent than for the first chroma component and the second chromacomponent. The video encoder and/or video decoder may generate thisasymmetric and/or unbalanced 3D lookup table by partitioning the lumacomponent into a different number of segments than the first and secondchroma components. In this example, table sizes may be up to 8×2×2.

The techniques of this disclosure are directed toward signaling ofinformation used to generate 3D lookup tables for color gamutscalability. According to the techniques, a video encoder may encodepartition information and/or color values of a 3D lookup table generatedfor color gamut scalability. A video decoder may decode the partitioninformation and/or color values to generate the 3D lookup table in orderto perform color gamut scalability. The techniques described in thisdisclosure may be particularly useful in signaling the information usedto generate asymmetric and/or unbalanced 3D lookup tables.

In one example of the disclosed techniques, a video decoder and/or videoencoder may generate a 3D lookup table with coarser partitioning forfirst and second chroma components and finer partitioning for a lumacomponent by partitioning each of the color components into a number ofoctants according to a base partition value, e.g., a maximal split depthfor the 3D lookup table, and then further partitioning each of theoctants of the luma component based on a luma partition value. In thisway, the chroma components of the 3D lookup table are partitioned intofewer octants (i.e., coarser partitioned) and the luma component of the3D lookup table is partitioned into more octants (i.e., finerpartitioned).

In one example, the luma partition value may be signaled in a bitstreamby the video encoder to the video decoder. In other examples, the basepartition value may also be signaled in the bitstream by the videoencoder to the video decoder. In other cases, the luma partition valuemay be derived by both the video encoder and the video decoder and/orthe base partition value may be a predefined value known at both thevideo encoder and the video decoder.

As an example, the base partition value is equal to 1 such that each ofthe first chroma, second chroma, and luma color components ispartitioned into a single octant, and the luma partition value is equalto 4 such that the single octant of the luma component is partitionedinto four octants, which results in a 3D lookup table of size 4×1×1. Asanother example, the base partition value is equal to 2 such that eachof the first chroma, second chroma, and luma color components ispartitioned into two octants, and the luma partition value is equal to 4such that each of the two octants of the luma component is partitionedinto four octants, which results in a 3D lookup table of size 8×2×2. Ascan be seen, a lower partition value results in a coarser partitioning(i.e., a smaller number of octants) for a color component.

According to the techniques, each of the color components may bepartitioned into one or more octants based on one or more of the basepartition value or the luma partition value. In this disclosure, theterm “octant” is defined as a three dimensional region that includeseight vertexes. In this disclosure, the terms “partition,” “octant,”“segment,” and “cuboid,” may be used interchangeably to describe thepartitioned regions of the color components of the 3D lookup table.

In addition, based on at least one of the first or second chromacomponents of the 3D lookup table being partitioned into more than oneoctant, i.e., the base partition value being greater than one, the videoencoder may signal a partitioning boundary for the one of the chromacomponents to the video decoder. The partitioning boundary defines anuneven partitioning of the one of the chroma components into two or moreoctants. In other words, one or both of the chroma components may not bepartitioned into two or more even or equally sized octants. In thiscase, for a given one of the chroma components, at least one of theoctants has a different size than the one or more other octants.According to the techniques of this disclosure, the video encoder onlysignals the partitioning boundary based on the condition that one of thechroma components is partitioned into more than one octant. Otherwise,the partition boundary is unnecessary and is not signaled to the videodecoder.

In another example of the disclosed techniques, a video encoder and/or avideo decoder may generate a 3D lookup table based on a number ofoctants for each of the luma, first chroma, and second chroma colorcomponents, and color values for each of the octants. As describedabove, in some cases, the number of octants for at least one of thecolor components of the 3D lookup table may also be signaled by thevideo encoder to the video decoder. In order for the video decoder todetermine the color values in the 3D lookup table, color mappingcoefficients for a linear color mapping function of the color values inthe 3D lookup table are signaled by the video encoder to the videodecoder. The linear color mapping function is used to convert color datain a first color gamut for a lower layer of video data to a second colorgamut for a higher layer of video data, and the color mappingcoefficients are weighting factors between color components of the lowerand higher layers of the video data. For each of the color components,one of the color mapping coefficients may be a key coefficient thatdefines a weighting factor between the same color component of the lowerand higher layers of the video data.

The color mapping coefficients of the linear color mapping function arederived as floating point values. Before signaling the color mappingcoefficients in a bitstream, the floating point values may be convertedto integer values. Although integer values may be less accurate thanfloating point values, the integer values are easier to signal andinteger operations are less computationally expensive than floatingpoint operations. The conversion may use a bit-depth for the integervalues based at least one of an input bit-depth or an output bit-depthof the 3D lookup table. In addition, the values of the color mappingcoefficients may be restricted to be within a given range based on apredefined fixed value or a value dependent on at least one of an inputbit-depth or an output bit-depth of the 3D lookup table.

One or more of the color mapping coefficients may be predicted such thatresidual values between original values of the color mappingcoefficients and predicted values of the color mapping coefficients areencoded in the bitstream. For example, for a first octant for each ofthe color components, the color mapping coefficients of the linear colormapping function may be predicted based on predefined fixed values. Inone example, a key coefficient of the linear color mapping function maybe predicted based on a predicted value equal to a predefined non-zerovalue, and any remaining color mapping coefficients may be predictedbased on a predicted value equal to zero. In this example, the colormapping coefficients of any remaining octants for each of the colorcomponents may be predicted based on predicted values from at least oneprevious octant, such as the first octant. In some cases, the residualvalues of the color mapping coefficients may be quantized based on adetermined quantization value. The video encoder may signal thedetermined quantization value for the video decoder to perform inversequantization to properly decode the color mapping coefficients.

Video coding standards include ITU-T H.261, ISO/IEC MPEG-1 Visual, ITU-TH.262 or ISO/IEC MPEG-2 Visual, ITU-T H.263, ISO/IEC MPEG-4 Visual andITU-T H.264 (also known as ISO/IEC MPEG-4 AVC), including its ScalableVideo Coding (SVC) and Multi-view Video Coding (MVC) extensions.

The design of a new video coding standard, namely HEVC, has beenfinalized by the Joint Collaboration Team on Video Coding (JCT-VC) ofITU-T Video Coding Experts Group (VCEG) and ISO/IEC Motion PictureExperts Group (MPEG). An HEVC draft specification referred to as HEVCWorking Draft 10 (WD10), Bross et al., “High efficiency video coding(HEVC) text specification draft 10 (for FDIS & Last Call),” JointCollaborative Team on Video Coding (JCT-VC) of ITU-T SG16 WP3 andISO/IEC JTC1/SC29/WG11, 12th Meeting: Geneva, CH, 14-23 Jan. 2013,JCTVC-L1003v34, is available fromhttp://phenix.int-evey.fr/jct/doc_end_user/documents/12_Geneva/wg11/JCTVC-L1003-v34.zip.The finalized HEVC standard is referred to as HEVC version 1.

A defect report, Wang et al., “High efficiency video coding (HEVC)Defect Report,” Joint Collaborative Team on Video Coding (JCT-VC) ofITU-T SG16 WP3 and ISO/IEC JTC1/SC29/WG11, 14th Meeting: Vienna, AT, 25Jul.-2 Aug. 2013, JCTVC-N1003v1, is available fromhttp://phenix.int-evey.fr/jct/doc_end_user/documents/14_Vienna/wg11/JCTVC-N1003-v1.zip.The finalized HEVC standard document is published as ITU-T H.265, SeriesH: Audiovisual and Multimedia Systems, Infrastructure of audiovisualservices—Coding of moving video, High efficiency video coding,Telecommunication Standardization Sector of InternationalTelecommunication Union (ITU), April 2013.

The multi-view extension to HEVC (MV-HEVC) and another HEVC extensionfor more advanced 3D video coding (3D-HEVC) are being developed by theJCT-3V. A draft specification of MV-HEVC, referred to as MV-HEVC WorkingDraft 5 (WD5), Tech et al., “MV-HEVC Draft Text 5,” Joint CollaborativeTeam on 3D Video Coding Extension Development (JCT-3V) of ITU-T SG16 WP3and ISO/IEC JTC1/SC29/WG11, 5th Meeting: Vienna, AT, 27 Jul.-2 Aug.2013, JCT3V-E1004v6, is available fromhttp://phenix.int-evry.fr/jct/doc_end_user/documents/5_Vienna/wg11/JCT3V-E1004-v6.zip.A draft specification of 3D-HEVC, referred to as 3D-HEVC Working Draft 1(WD1) and described in Tech et al., “3D-HEVC Draft Text 1,” JointCollaborative Team on 3D Video Coding Extension Development (JCT-3V) ofITU-T SG 16 WP 3 and ISO/IEC JTC 1/SC 29/WG 11, 5th Meeting: Vienna, AT,27 Jul.-2 Aug. 2013, JCT3V-E1001v3, is available fromhttp://phenix.it-sudparis.eu/jct2/doc_end_user/documents/5_Vienna/wg11/JCT3V-E1001-v3.zip.

The scalable extension to HEVC (SHVC) is being developed by the JCT-VC.A draft specification of SHVC, referred to as SHVC Working Draft 3(WD3), Chen et al., “SHVC Draft 3,” Joint Collaborative Team on VideoCoding (JCT-VC) of ITU-T SG16 WP3 and ISO/IEC JTC1/SC29/WG11, 14thMeeting: Vienna, AT, 25 Jul.-2 Aug. 2013, JCTVC-N1008v3, is availablefromhttp://phenix.int-evey.fr/jct/doc_end_user/documents/14_Vienna/wg11/JCTVC-N1008-v3.zip.

FIG. 1 is a block diagram illustrating an example video encoding anddecoding system 10 that may utilize techniques for 3D lookup table basedcolor gamut scalability. As shown in FIG. 1, system 10 includes a sourcedevice 12 that provides encoded video data to be decoded at a later timeby a destination device 14. In particular, source device 12 provides thevideo data to destination device 14 via a computer-readable medium 16.Source device 12 and destination device 14 may comprise any of a widerange of devices, including desktop computers, notebook (i.e., laptop)computers, tablet computers, set-top boxes, telephone handsets such asso-called “smart” phones, so-called “smart” pads, televisions, cameras,display devices, digital media players, video gaming consoles, videostreaming device, or the like. In some cases, source device 12 anddestination device 14 may be equipped for wireless communication.

Destination device 14 may receive the encoded video data to be decodedvia computer-readable medium 16. Computer-readable medium 16 maycomprise any type of medium or device capable of moving the encodedvideo data from source device 12 to destination device 14. In oneexample, computer-readable medium 16 may comprise a communication mediumto enable source device 12 to transmit encoded video data directly todestination device 14 in real-time. The encoded video data may bemodulated according to a communication standard, such as a wirelesscommunication protocol, and transmitted to destination device 14. Thecommunication medium may comprise any wireless or wired communicationmedium, such as a radio frequency (RF) spectrum or one or more physicaltransmission lines. The communication medium may form part of apacket-based network, such as a local area network, a wide-area network,or a global network such as the Internet. The communication medium mayinclude routers, switches, base stations, or any other equipment thatmay be useful to facilitate communication from source device 12 todestination device 14.

In some examples, encoded data may be output from output interface 22 toa storage device. Similarly, encoded data may be accessed from thestorage device by input interface. The storage device may include any ofa variety of distributed or locally accessed data storage media such asa hard drive, Blu-ray discs, DVDs, CD-ROMs, flash memory, volatile ornon-volatile memory, or any other suitable digital storage media forstoring encoded video data. In a further example, the storage device maycorrespond to a file server or another intermediate storage device thatmay store the encoded video generated by source device 12. Destinationdevice 14 may access stored video data from the storage device viastreaming or download. The file server may be any type of server capableof storing encoded video data and transmitting that encoded video datato the destination device 14. Example file servers include a web server(e.g., for a website), an FTP server, network attached storage (NAS)devices, or a local disk drive. Destination device 14 may access theencoded video data through any standard data connection, including anInternet connection. This may include a wireless channel (e.g., a Wi-Ficonnection), a wired connection (e.g., DSL, cable modem, etc.), or acombination of both that is suitable for accessing encoded video datastored on a file server. The transmission of encoded video data from thestorage device may be a streaming transmission, a download transmission,or a combination thereof.

The techniques of this disclosure are not necessarily limited towireless applications or settings. The techniques may be applied tovideo coding in support of any of a variety of multimedia applications,such as over-the-air television broadcasts, cable televisiontransmissions, satellite television transmissions, Internet streamingvideo transmissions, such as dynamic adaptive streaming over HTTP(DASH), digital video that is encoded onto a data storage medium,decoding of digital video stored on a data storage medium, or otherapplications. In some examples, system 10 may be configured to supportone-way or two-way video transmission to support applications such asvideo streaming, video playback, video broadcasting, and/or videotelephony.

In the example of FIG. 1, source device 12 includes video source 18,video encoder 20, and output interface 22. Destination device 14includes input interface 28, video decoder 30, and display device 32. Inaccordance with this disclosure, video encoder 20 of source device 12may be configured to apply the techniques for processing video data inparallel. In other examples, a source device and a destination devicemay include other components or arrangements. For example, source device12 may receive video data from an external video source 18, such as anexternal camera. Likewise, destination device 14 may interface with anexternal display device, rather than including an integrated displaydevice.

The illustrated system 10 of FIG. 1 is merely one example. Techniquesfor processing video data in parallel may be performed by any digitalvideo encoding and/or decoding device. Although generally the techniquesof this disclosure are performed by a video encoding device, thetechniques may also be performed by a video encoder/decoder, typicallyreferred to as a “CODEC.” Moreover, the techniques of this disclosuremay also be performed by a video preprocessor. Source device 12 anddestination device 14 are merely examples of such coding devices inwhich source device 12 generates coded video data for transmission todestination device 14. In some examples, devices 12, 14 may operate in asubstantially symmetrical manner such that each of devices 12, 14include video encoding and decoding components. Hence, system 10 maysupport one-way or two-way video transmission between video devices 12,14, e.g., for video streaming, video playback, video broadcasting, orvideo telephony.

Video source 18 of source device 12 may include a video capture device,such as a video camera, a video archive containing previously capturedvideo, and/or a video feed interface to receive video from a videocontent provider. As a further alternative, video source 18 may generatecomputer graphics-based data as the source video, or a combination oflive video, archived video, and computer-generated video. In some cases,if video source 18 is a video camera, source device 12 and destinationdevice 14 may form so-called camera phones or video phones. As mentionedabove, however, the techniques described in this disclosure may beapplicable to video coding in general, and may be applied to wirelessand/or wired applications. In each case, the captured, pre-captured, orcomputer-generated video may be encoded by video encoder 20. The encodedvideo information may then be output by output interface 22 onto acomputer-readable medium 16.

Computer-readable medium 16 may include transient media, such as awireless broadcast or wired network transmission, or storage media (thatis, non-transitory storage media), such as a hard disk, flash drive,compact disc, digital video disc, Blu-ray disc, or othercomputer-readable media. In some examples, a network server (not shown)may receive encoded video data from source device 12 and provide theencoded video data to destination device 14, e.g., via networktransmission. Similarly, a computing device of a medium productionfacility, such as a disc stamping facility, may receive encoded videodata from source device 12 and produce a disc containing the encodedvideo data. Therefore, computer-readable medium 16 may be understood toinclude one or more computer-readable media of various forms, in variousexamples.

Input interface 28 of destination device 14 receives information fromcomputer-readable medium 16. The information of computer-readable medium16 may include syntax information defined by video encoder 20, which isalso used by video decoder 30, that includes syntax elements thatdescribe characteristics and/or processing of blocks and other codedunits, e.g., groups of pictures (GOPs). Display device 32 displays thedecoded video data to a user, and may comprise any of a variety ofdisplay devices such as a cathode ray tube (CRT), a liquid crystaldisplay (LCD), a plasma display, an organic light emitting diode (OLED)display, or another type of display device.

Video encoder 20 and video decoder 30 each may be implemented as any ofa variety of suitable encoder circuitry, such as one or moremicroprocessors, digital signal processors (DSPs), application specificintegrated circuits (ASICs), field programmable gate arrays (FPGAs),discrete logic, software, hardware, firmware or any combinationsthereof. When the techniques are implemented partially in software, adevice may store instructions for the software in a suitable,non-transitory computer-readable medium and execute the instructions inhardware using one or more processors to perform the techniques of thisdisclosure. Each of video encoder 20 and video decoder 30 may beincluded in one or more encoders or decoders, either of which may beintegrated as part of a combined encoder/decoder (CODEC) in a respectivedevice.

In some examples, video encoder 20 and video decoder 30 operateaccording to a video compression standard, such as ISO/IEC MPEG-4 Visualand ITU-T H.264 (also known as ISO/IEC MPEG-4 AVC), including itsScalable Video Coding (SVC) extension, Multi-view Video Coding (MVC)extension, and MVC-based three-dimensional video (3DV) extension. Insome instances, any bitstream conforming to MVC-based 3DV alwayscontains a sub-bitstream that is compliant to a MVC profile, e.g.,stereo high profile. Furthermore, there is an ongoing effort to generatea 3DV coding extension to H.264/AVC, namely AVC-based 3DV. Otherexamples of video coding standards include ITU-T H.261, ISO/IEC MPEG-1Visual, ITU-T H.262 or ISO/IEC MPEG-2 Visual, ITU-T H.263, ISO/IECMPEG-4 Visual, and ITU-T H.264, ISO/IEC Visual.

In the example of FIG. 1, video encoder 20 and video decoder 30 mayoperate according to the High Efficiency Video Coding (HEVC) standardfinalized by the Joint Collaboration Team on Video Coding (JCT-VC) ofITU-T Video Coding Experts Group (VCEG) and ISO/IEC Motion PictureExperts Group (MPEG). The HEVC draft specification, referenced above, isreferred to as HEVC Working Draft 10 (WD10), and the finalized versionof the HEVC standard is referred to as HEVC version 1. The MV-HEVC and3D-HEVC are being developed by the JCT-3V. A recent draft specificationof MV-HEVC is referred to as MV-HEVC WD5, and a recent draftspecification of 3D-HEVC is referred to as 3D-HEVC WD1. The SHVC isbeing developed by the JCT-VC. A recent draft specification of SHVC isreferred to as SHVC WD3.

In HEVC and other video coding standards, a video sequence typicallyincludes a series of pictures. Pictures may also be referred to as“frames.” A picture may include three sample arrays, denoted SL, Scb,and Scr. SL is a two-dimensional array (i.e., a block) of luma samples.Scb is a two-dimensional array of Cb chrominance samples. Scr is atwo-dimensional array of Cr chrominance samples. Chrominance samples mayalso be referred to herein as “chroma” samples. In other instances, apicture may be monochrome and may only include an array of luma samples.

Video encoder 20 may generate a set of coding tree units (CTUs). Each ofthe CTUs may comprise a coding tree block of luma samples, twocorresponding coding tree blocks of chroma samples, and syntaxstructures used to code the samples of the coding tree blocks. In amonochrome picture or a picture that has three separate color planes, aCTU may comprise a single coding tree block and syntax structures usedto code the samples of the coding tree block. A coding tree block may bean N×N block of samples. A CTU may also be referred to as a “tree block”or a “largest coding unit” (LCU). The CTUs of HEVC may be broadlyanalogous to the macroblocks of other video coding standards, such asH.264/AVC. However, a CTU is not necessarily limited to a particularsize and may include one or more coding units (CUs). A slice may includean integer number of CTUs ordered consecutively in the raster scan.

This disclosure may use the term “video unit” or “video block” to referto one or more blocks of samples and syntax structures used to codesamples of the one or more blocks of samples. Example types of videounits may include CTUs, CUs, PUs, transform units (TUs) in HEVC, ormacroblocks, macroblock partitions, and so on in other video codingstandards.

To generate a coded CTU, video encoder 20 may recursively performquad-tree partitioning on the coding tree blocks of a CTU to divide thecoding tree blocks into coding blocks, hence the name “coding treeunits.” A coding block is an N×N block of samples. A CU may comprise acoding block of luma samples and two corresponding coding blocks ofchroma samples of a picture that has a luma sample array, a Cb samplearray and a Cr sample array, and syntax structures used to code thesamples of the coding blocks. In a monochrome picture or a picture thathas three separate color planes, a CU may comprise a single coding blockand syntax structures used to code the samples of the coding block.

Video encoder 20 may partition a coding block of a CU into one or moreprediction blocks. A prediction block may be a rectangular (i.e., squareor non-square) block of samples on which the same prediction is applied.A prediction unit (PU) of a CU may comprise a prediction block of lumasamples, two corresponding prediction blocks of chroma samples of apicture, and syntax structures used to predict the prediction blocksamples. In a monochrome picture or a picture that have three separatecolor planes, a PU may comprise a single prediction block and syntaxstructures used to predict the prediction block samples. Video encoder20 may generate predictive luma, Cb and Cr blocks for luma, Cb and Crprediction blocks of each PU of the CU.

Video encoder 20 may use intra prediction or inter prediction togenerate the predictive blocks for a PU. If video encoder 20 uses intraprediction to generate the predictive blocks of a PU, video encoder 20may generate the predictive blocks of the PU based on decoded samples ofthe picture associated with the PU.

If video encoder 20 uses inter prediction to generate the predictiveblocks of a PU, video encoder 20 may generate the predictive blocks ofthe PU based on decoded samples of one or more pictures other than thepicture associated with the PU. Inter prediction may be uni-directionalinter prediction (i.e., uni-prediction) or bi-directional interprediction (i.e., bi-prediction). To perform uni-prediction orbi-prediction, video encoder 20 may generate a first reference picturelist (RefPicList0) and a second reference picture list (RefPicList1) fora current slice.

Each of the reference picture lists may include one or more referencepictures. When using uni-prediction, video encoder 20 may search thereference pictures in either or both RefPicList0 and RefPicList1 todetermine a reference location within a reference picture. Furthermore,when using uni-prediction, video encoder 20 may generate, based at leastin part on samples corresponding to the reference location, thepredictive sample blocks for the PU. Moreover, when usinguni-prediction, video encoder 20 may generate a single motion vectorthat indicates a spatial displacement between a prediction block of thePU and the reference location. To indicate the spatial displacementbetween a prediction block of the PU and the reference location, amotion vector may include a horizontal component specifying a horizontaldisplacement between the prediction block of the PU and the referencelocation and may include a vertical component specifying a verticaldisplacement between the prediction block of the PU and the referencelocation.

When using bi-prediction to encode a PU, video encoder 20 may determinea first reference location in a reference picture in RefPicList0 and asecond reference location in a reference picture in RefPicList1. Videoencoder 20 may then generate, based at least in part on samplescorresponding to the first and second reference locations, thepredictive blocks for the PU. Moreover, when using bi-prediction toencode the PU, video encoder 20 may generate a first motion indicating aspatial displacement between a sample block of the PU and the firstreference location and a second motion indicating a spatial displacementbetween the prediction block of the PU and the second referencelocation.

After video encoder 20 generates predictive luma, Cb, and Cr blocks forone or more PUs of a CU, video encoder 20 may generate a luma residualblock for the CU. Each sample in the CU's luma residual block indicatesa difference between a luma sample in one of the CU's predictive lumablocks and a corresponding sample in the CU's original luma codingblock. In addition, video encoder 20 may generate a Cb residual blockfor the CU. Each sample in the CU's Cb residual block may indicate adifference between a Cb sample in one of the CU's predictive Cb blocksand a corresponding sample in the CU's original Cb coding block. Videoencoder 20 may also generate a Cr residual block for the CU. Each samplein the CU's Cr residual block may indicate a difference between a Crsample in one of the CU's predictive Cr blocks and a correspondingsample in the CU's original Cr coding block.

Furthermore, video encoder 20 may use quad-tree partitioning todecompose the luma, Cb and, Cr residual blocks of a CU into one or moreluma, Cb, and Cr transform blocks. A transform block may be arectangular block of samples on which the same transform is applied. Atransform unit (TU) of a CU may comprise a transform block of lumasamples, two corresponding transform blocks of chroma samples, andsyntax structures used to transform the transform block samples. In amonochrome picture or a picture that has three separate color planes, aTU may comprise a single transform block and syntax structures used totransform the transform block samples. Thus, each TU of a CU may beassociated with a luma transform block, a Cb transform block, and a Crtransform block. The luma transform block associated with the TU may bea sub-block of the CU's luma residual block. The Cb transform block maybe a sub-block of the CU's Cb residual block. The Cr transform block maybe a sub-block of the CU's Cr residual block.

Video encoder 20 may apply one or more transforms to a luma transformblock of a TU to generate a luma coefficient block for the TU. Acoefficient block may be a two-dimensional array of transformcoefficients. A transform coefficient may be a scalar quantity. Videoencoder 20 may apply one or more transforms to a Cb transform block of aTU to generate a Cb coefficient block for the TU. Video encoder 20 mayapply one or more transforms to a Cr transform block of a TU to generatea Cr coefficient block for the TU.

After generating a coefficient block (e.g., a luma coefficient block, aCb coefficient block or a Cr coefficient block), video encoder 20 mayquantize the coefficient block. Quantization generally refers to aprocess in which transform coefficients are quantized to possibly reducethe amount of data used to represent the transform coefficients,providing further compression. Furthermore, video encoder 20 may inversequantize transform coefficients and apply an inverse transform to thetransform coefficients in order to reconstruct transform blocks of TUsof CUs of a picture. Video encoder 20 may use the reconstructedtransform blocks of TUs of a CU and the predictive blocks of PUs of theCU to reconstruct coding blocks of the CU. By reconstructing the codingblocks of each CU of a picture, video encoder 20 may reconstruct thepicture. Video encoder 20 may store reconstructed pictures in a decodedpicture buffer (DPB). Video encoder 20 may use reconstructed pictures inthe DPB for inter prediction and intra prediction.

After video encoder 20 quantizes a coefficient block, video encoder 20may entropy encode syntax elements that indicate the quantized transformcoefficients. For example, video encoder 20 may perform Context-AdaptiveBinary Arithmetic Coding (CABAC) on the syntax elements indicating thequantized transform coefficients. Video encoder 20 may output theentropy-encoded syntax elements in a bitstream.

Video encoder 20 may output a bitstream that includes a sequence of bitsthat forms a representation of coded pictures and associated data. Thebitstream may comprise a sequence of network abstraction layer (NAL)units. Each of the NAL units includes a NAL unit header and encapsulatesa raw byte sequence payload (RBSP). The NAL unit header may include asyntax element that indicates a NAL unit type code. The NAL unit typecode specified by the NAL unit header of a NAL unit indicates the typeof the NAL unit. A RBSP may be a syntax structure containing an integernumber of bytes that is encapsulated within a NAL unit. In someinstances, an RBSP includes zero bits.

Different types of NAL units may encapsulate different types of RBSPs.For example, a first type of NAL unit may encapsulate a RBSP for apicture parameter set (PPS), a second type of NAL unit may encapsulate aRBSP for a coded slice, a third type of NAL unit may encapsulate a RBSPfor Supplemental Enhancement Information (SEI), and so on. A PPS is asyntax structure that may contain syntax elements that apply to zero ormore entire coded pictures. NAL units that encapsulate RBSPs for videocoding data (as opposed to RBSPs for parameter sets and SEI messages)may be referred to as video coding layer (VCL) NAL units. A NAL unitthat encapsulates a coded slice may be referred to herein as a codedslice NAL unit. A RBSP for a coded slice may include a slice header andslice data.

Video decoder 30 may receive a bitstream. In addition, video decoder 30may parse the bitstream to decode syntax elements from the bitstream.Video decoder 30 may reconstruct the pictures of the video data based atleast in part on the syntax elements decoded from the bitstream. Theprocess to reconstruct the video data may be generally reciprocal to theprocess performed by video encoder 20. For instance, video decoder 30may use motion vectors of PUs to determine predictive blocks for the PUsof a current CU. Video decoder 30 may use a motion vector or motionvectors of PUs to generate predictive blocks for the PUs.

In addition, video decoder 30 may inverse quantize coefficient blocksassociated with TUs of the current CU. Video decoder 30 may performinverse transforms on the coefficient blocks to reconstruct transformblocks associated with the TUs of the current CU. Video decoder 30 mayreconstruct the coding blocks of the current CU by adding the samples ofthe predictive sample blocks for PUs of the current CU to correspondingsamples of the transform blocks of the TUs of the current CU. Byreconstructing the coding blocks for each CU of a picture, video decoder30 may reconstruct the picture. Video decoder 30 may store decodedpictures in a decoded picture buffer for output and/or for use indecoding other pictures.

In MV-HEVC, 3D-HEVC, and SHVC, a video encoder may generate amulti-layer bitstream that comprises a series of network abstractionlayer (NAL) units. Different NAL units of the bitstream may beassociated with different layers of the bitstream. A layer may bedefined as a set of video coding layer (VCL) NAL units and associatednon-VCL NAL units that have the same layer identifier. A layer may beequivalent to a view in multi-view video coding. In multi-view videocoding, a layer can contain all view components of the same layer withdifferent time instances. Each view component may be a coded picture ofthe video scene belonging to a specific view at a specific timeinstance. In 3D video coding, a layer may contain either all coded depthpictures of a specific view or coded texture pictures of a specificview. Similarly, in the context of scalable video coding, a layertypically corresponds to coded pictures having video characteristicsdifferent from coded pictures in other layers. Such videocharacteristics typically include spatial resolution and quality level(Signal-to-Noise Ratio). In HEVC and its extensions, temporalscalability may be achieved within one layer by defining a group ofpictures with a particular temporal level as a sub-layer.

For each respective layer of the bitstream, data in a lower layer may bedecoded without reference to data in any higher layer. In scalable videocoding, for example, data in a base layer may be decoded withoutreference to data in an enhancement layer. NAL units only encapsulatedata of a single layer. In SHVC, a view may be referred to as a “baselayer” if a video decoder can decode pictures in the view withoutreference to data of any other layer. The base layer may conform to theHEVC base specification. Thus, NAL units encapsulating data of thehighest remaining layer of the bitstream may be removed from thebitstream without affecting the decodability of data in the remaininglayers of the bitstream. In MV-HEVC and 3D-HEVC, higher layers mayinclude additional view components. In SHVC, higher layers may includesignal to noise ratio (SNR) enhancement data, spatial enhancement data,and/or temporal enhancement data.

In some examples, data in a higher layer may be decoded with referenceto data in one or more lower layers. The lower layers may be used asreference pictures to compress the higher layer using inter-layerprediction. The data of the lower layers may be up-sampled to have thesame resolution as the higher layers. In general, video encoder 20 andvideo decoder 30 may perform inter-layer prediction in a similar manneras inter prediction described above, except one or more up-sampled lowerlayers may be used as reference pictures as opposed to one or moreneighboring pictures.

FIG. 2 is a conceptual illustration showing an example of scalability inthree different dimensions. In a scalable video coding structure,scalabilities are enabled in three dimensions. In the example of FIG. 2,the scalabilities are enabled in a spatial (S) dimension 100, a temporal(T) dimension 102, and a signal-to-noise ratio (SNR) or quality (Q)dimension 104. In the temporal dimension 102, frame rates with 7.5 Hz(T0), 15 Hz (T1) or 30 Hz (T2), for example, may be supported bytemporal scalability. When spatial scalability is supported, differentresolutions such as QCIF (S0), CIF (S1) and 4CIF (S2), for example, areenabled in the spatial dimension 100. For each specific spatialresolution and frame rate, SNR layers (Q1) can be added in the SNRdimension 104 to improve the picture quality.

Once video content has been encoded in such a scalable way, an extractortool may be used to adapt the actual delivered content according toapplication requirements, which are dependent e.g., on the clients orthe transmission channel. In the example shown in FIG. 2, each cubiccontains pictures with the same frame rate (temporal level), spatialresolution, and SNR layers. Better representation may be achieved byadding cubes (i.e., pictures) in any of dimensions 100, 102 or 104.Combined scalability is supported when there are two, three or even morescalabilities enabled.

In scalable video coding standards, such as the SVC extension to H.264or SHVC, the pictures with the lowest spatial and SNR layer arecompatible with the single layer video codec, and the pictures at thelowest temporal level form the temporal base layer, which may beenhanced with pictures at higher temporal levels. In addition to thebase layer, several spatial and/or SNR enhancement layers may be addedto provide spatial and/or quality scalabilities. Each spatial or SNRenhancement layer itself may be temporally scalable, with the sametemporal scalability structure as the base layer. For one spatial or SNRenhancement layer, the lower layer it depends on may be referred as thebase layer of that specific spatial or SNR enhancement layer.

FIG. 3 is a conceptual illustration showing an example structure 110 ofa scalable video coding bitstream. The bitstream structure 110 includesa layer 0 112 that includes pictures or slices I0, P4 and P8, and alayer 1 114 that includes pictures or slices B2, B6 and B10. Inaddition, bitstream structure 110 includes a layer 2 116 and a layer 3117 that each includes pictures 0, 2, 4, 6, 8 and 10, and a layer 4 118that includes pictures 0 through 11.

A base layer has the lowest spatial and quality layer (i.e., pictures inlayer 0 112 and layer 1 114 with QCIF resolution). Among them, thosepictures of the lowest temporal level form the temporal base layer, asshown in layer 0 112 of FIG. 3. The temporal base layer (layer 0) 112can be enhanced with pictures of a higher temporal level, e.g., layer 1114 with frame rate of 15 Hz or layer 4 118 with frame rate of 30 Hz.

In addition to the base layer 112, 114, several spatial and/or SNRenhancement layers may be added to provide spatial and/or qualityscalabilities. For example, layer 2 116 with CIF resolution may be aspatial enhancement layer to base layer 112, 114. In another example,layer 3 117 may be an SNR enhancement layer to base layer 112, 114 andlayer 2 116. As shown in FIG. 3, each spatial or SNR enhancement layeritself may be temporally scalable, with the same temporal scalabilitystructure as the base layer 112, 114. In addition, an enhancement layermay enhance both spatial resolution and frame rate. For example, layer 4118 provides a 4CIF resolution enhancement layer, which furtherincreases the frame rate from 15 Hz to 30 Hz.

FIG. 4 is a conceptual illustration showing example scalable videocoding access units 120A-120E (“access units 120”) in bitstream order.As shown in FIG. 4, the coded pictures or slices in the same timeinstance are successive in the bitstream order and form one access unitin the context of a scalable video coding standard, such as the SVCextension to H.264 or SHVC. The access units 120 then follow thedecoding order, which could be different from the display order anddetermined, for example, by the temporal prediction relationship betweenaccess units 120.

For example, access unit 120A includes picture I0 from layer 0 112,picture 0 from layer 2 116, picture 0 from layer 3 117, and picture 0from layer 4 118. Access unit 120B includes picture P4 from layer 0 112,picture 4 from layer 2 116, picture 4 from layer 3 117, and picture 4from layer 4 118. Access unit 120C includes picture B2 from layer 1 114,picture 2 from layer 2 116, picture 2 from layer 3 117, and picture 2from layer 4 118. Access unit 120D includes picture 1 from layer 4 118,and access unit 120E includes picture 3 from layer 4 118.

FIG. 5 is a block diagram illustrating an example 3-layer SHVC encoder122. As illustrated in FIG. 5, SHVC encoder 122 includes a base layerencoder 124, a first enhancement layer encoder 125 and a secondenhancement layer encoder 126. In high-level syntax only SHVC, there areno new block level coding tools when compared to HEVC single layercoding. In SHVC, only slice and above level syntax changes and picturelevel operation, such as picture filtering or up-sampling, are allowed.

To reduce the redundancy between layers, up-sampled co-located referencelayer pictures for a lower/base layer may generated and stored in areference buffer for a higher/enhancement layer so that inter-layerprediction may be achieved in the same way as inter-frame predictionwithin a single layer. As illustrated in FIG. 5, a resampled inter-layerreference (ILR) picture 128 is generated from a reference picture inbase layer encoder 124 and stored in first enhancement layer encoder125. Similarly, a resampled ILR picture 129 is generated from areference picture in first enhancement layer encoder 125 and stored insecond enhancement layer encoder 126. In SHVC WD3, the ILR picture ismarked as a long term reference picture for the enhancement layer. Themotion vector difference associated with an inter-layer referencepicture is constrained to zero.

The upcoming deployment of ultra-high definition television (UHDTV)devices and content will use a different color gamut than legacydevices. Specifically, HD uses the BT.709 recommendation, ITU-RRecommendation BT.709 “Parameter values for the HDTV standards forproduction and international programme exchange” December 2010, whileUHDTV will use the BT.2020 recommendation, ITU-R Recommendation BT.2020“Parameter values for UHDTV systems for production and internationalprogramme exchange” April 2012. A color gamut comprises a complete rangeof colors that can be reproduced for an image, e.g., in a picture,slice, block or layer of video data. A key difference between thesesystems is that the color gamut of UHDTV is significantly larger thanHD. It is asserted that UHDTV will provide a more life-like or realisticviewing experience, which is consistent with other UHDTVcharacteristics, such as high resolution.

FIG. 6 is a graph illustrating an example color gamut of a sample videosequence 130. As illustrated in FIG. 6, the SWG1 sample video sequence130 is indicated as a cluster of dots within a line outline of the UHDcolor gamut BT.2020 132. For comparison purposes, an outline of the HDcolor gamut BT.709 134 and an outline of the International Commission onIllumination (CIE)-XYZ linear color space 136 overlays the SWG1 samplevideo sequence 130. It is easily observed from FIG. 6 that the UHD colorgamut BT.2020 132 is much larger than the HD color gamut BT.709 134.Note the number of pixels in the SWG1 sample video sequence 130 thatfall outside of the BT.709 color gamut 134.

FIG. 7 is a block diagram illustrating conversion from HD color gamutBT.709 134 to UHD color gamut BT.2020 132. Both the HD color gamutBT.709 134 and the UHD color gamut BT.2020 132 define representations ofcolor pixels in luma and chroma components (e.g., YCbCr or YUV). Eachcolor gamut defines conversion to and from the CIE-XYZ linear colorspace 136. This common intermediate color space may be used to definethe conversion of the luma and chroma values in the HD color gamutBT.709 134 to corresponding luma and chroma values in the UHD colorgamut BT.2020 132.

More details regarding the color gamut of the sample sequenceillustrated in FIG. 6 and the color gamut conversion illustrated in FIG.7 may be found in L. Kerofsky, A. Segall, S.-H. Kim, K. Misra, “ColorGamut Scalable Video Coding: New Results,” JCTVC-L0334, Geneva, CH,14-23 Jan. 2013 (hereinafter referred to as “JCTVC-L0334”).

FIG. 8 is a block diagram illustrating a color gamut scalable coder 140including a color prediction processing unit 144 that may generate aninter-layer reference picture when a base layer color gamut and anenhancement layer color gamut are different. Color prediction processingunit 144 may be used by a video coder, such as video encoder 20 or videodecoder 30 from FIG. 1, to perform color gamut scalable video coding, inwhich the color gamut of the base and enhancement layer is different.

In the example illustrated in FIG. 8, a base layer coding loop 142performs video coding of pictures that include color data in a firstcolor gamut, e.g., BT.709, and an enhancement layer coding loop 146performs video coding of pictures that include color data in a secondcolor gamut, e.g., BT.2020. Color prediction processing unit 144performs color prediction to map or convert color data of a base layerreference picture in the first color gamut to the second color gamut,and generates an inter-layer reference picture for the enhancement layerbased on the mapped color data of the base layer reference picture.

To achieve high coding efficiency, color prediction processing unit 144is configured to perform specific color prediction when generatinginter-layer reference pictures. As described in more detail below, colorprediction processing unit 144 may be configured to perform colorprediction according to any of a linear prediction model, a piecewiselinear prediction model, or a 3D lookup table based color predictionmodel.

A linear prediction model is proposed in JCTVC-L0334, referenced above.Generally, the color prediction process of the linear prediction modelmay be described as a gain and offset model. The linear prediction modeloperates on individual color planes. To facilitate integer calculation,a parameter describes the number of fractional bits used in thecalculation using the parameter numFractionBits. For each channel, again[c] and offset[c] are specified. The linear prediction model isdefined as follows:Pred[c][x][y]=(gain[c]*In[x][y]+(1<<(numFractionBits−1))>>numFractionBits+offset[c]

A piecewise linear prediction model is proposed in C. Auyeung, K. Sato,“AHG14: Color gamut scalable video coding with piecewise linearpredictions and shift-offset model,” JCTVC-N0271, Vienna, Austria, July2013, based on JCTVC-L0334, referenced above. The color predictionprocess of the piecewise linear prediction model may also be describedas a gain and offset model. The piecewise linear prediction model isdefined as follows:Let d[c][x][y]=In[c][x][y]−knot[c].If d[c][x][y]<=0Pred[c][x][y]=(gain1[c]*d[c][x][y]+offset[c]+(1<<(numFractionBits−1)))>>numFractionBitselsePred[c][x][y]=(gain2[c]*d[c][x][y]+offset[c]+(1<<(numFractionBits−1)))>>numFractionBitsThe prediction parameters knot[c], offset[c], gain1[c], and gain2[c] maybe encoded in the bitstream.

FIGS. 9(a) and 9(b) are conceptual illustrations showing an example 3Dlookup table 150 for color gamut scalability. A 3D lookup table basedcolor prediction model is proposed in P. Bordes, P. Andrivon, F. Hiron,“AHG14: Color Gamut Scalable Video Coding using 3D LUT: New Results,”JCTVC-N0168, Vienna, Austria, July 2013 (hereinafter referred to as“JCTVC-N0168”). The principle of the 3D lookup table for color gamutscalability is depicted in FIGS. 9(a) and 9(b). The 3D lookup table 150can be considered as a sub-sampling of a first 3D color space, e.g., HDcolor gamut BT.709, where each vertex is associated with a color triplet(y, u, v) corresponding to a second 3D color space (i.e., predicted)values, e.g., UHD color gamut BT.2020).

In general, the first color gamut may be partitioned into octants orcuboids in each color dimension (i.e., Y, U, and V), and the vertices ofthe octants are associated with the color triplet corresponding to thesecond color gamut and used to populate 3D lookup table 150. The numberof vertices or segments in each color dimension indicates the size of 3Dlookup table. FIG. 9(a) illustrates the vertices or intersecting latticepoints of the octants in each color dimension. FIG. 9(b) illustrates thedifferent color values associated with each of the vertices. Asillustrated, in FIG. 9(a) each color dimension has four vertices and inFIG. 9(b) each color dimension includes four color values.

FIG. 10 is a conceptual illustration showing tri-linear interpolationwith a 3D lookup table 152 for color gamut scalability. For a given baselayer color sample in the first color gamut, the computation of itsprediction in the second color gamut for an enhancement layer is madeusing tri-linear interpolation according to the following equation:

$\overset{\_}{{value}_{y}} = {K \times {\sum\limits_{{i = 0},1}\;{\sum\limits_{{j = 0},1}\;{\sum\limits_{{k = 0},1}\;{{s_{i}(y)} \times {s_{j}(u)} \times {s_{k}(v)} \times {{{{{LUT}\left\lbrack y_{i} \right\rbrack}\left\lbrack u_{j} \right\rbrack}\left\lbrack v_{k} \right\rbrack} \cdot y}}}}}}$${{Where}\text{:}\mspace{14mu} K} = \frac{1}{\left( {y_{1} - y_{0}} \right) \times \left( {u_{1} - u_{0}} \right) \times \left( {v_{1} - v_{0}} \right)}$S₀(y) = y₁ − y  and  S₁(y) = y − y₀y₀  is  the  index  of  the  nearest  sub-sampled  vertex  inferior  to  y, y₁  is  the  index  of  the  nearest  sub-sampled  vertex  superior  to  y.More details of the 3D lookup table illustrated in FIG. 9 and thetri-linear interpolation with the 3D lookup table illustrated in FIG. 10may be found in JCTVC-N0168, referenced above.

FIG. 11 is a conceptual illustration showing tetrahedral interpolationwith a 3D lookup table 154 for color gamut scalability. The tetrahedralinterpolation may be used instead of the tri-linear interpolationdescribed above to reduce the computational complexity of the 3D lookuptable.

FIG. 12 is a conceptual illustration showing six examples oftetrahedrons 156A-156F (collectively “tetrahedrons 156”) used toencompass a point P of a 3D lookup table to be interpolated usingtetrahedral interpolation. In the example of FIG. 12, there are sixchoices to determine the tetrahedron containing the point P to beinterpolated in an octant of the 3D lookup table given that vertexes P₀and P₇ have to be included in the tetrahedron. Using tetrahedralinterpolation, the 3D lookup table may be designed for a fast decisioninstead of checking the relationship of each two components: y and u, yand v, u and v.

In some examples, a separate 3D lookup table may be generated for eachof the color components, i.e., a luma (Y) component, a first chroma (U)component and a second chroma (V) component. Each of the 3D lookuptables includes a luma (Y) dimension, a first chroma (U) dimension and asecond chroma (V) dimension, and is indexed using the three independentcolor components (Y, U, V).

In one example, a mapping function may be defined for each colorcomponent based on the 3D lookup table. An example mapping function fora luma (Y) pixel value is presented in the following equation:Y _(E) =LUT _(Y)(Y _(B) ,U _(B) ,V _(B))*Y _(B) +LUT _(U)(Y _(B) ,U _(B),V _(B))*U _(B) +LUT _(v)(Y _(B) ,U _(B) ,V _(B))*V _(B) +LUT _(C)(Y_(B) ,U _(B) ,V _(B))In the above equation, Y_(E) represents the luma pixel value in theenhancement layer, (Y_(B), U_(B), V_(B)) represents a base layer pixelvalue, and LUT_(Y), LUT_(U), LUT_(V) and LUT_(C) represent the 3D lookuptable for each color component Y, U, V, and a constant, respectively.Similar mapping functions may be defined for a first chroma (U) pixelvalue and a second chroma (V) pixel value in the enhancement layer.

In general, 3D lookup table based color gamut scalability results ingood coding performance. The size of the 3D lookup table may be concern,however, since the 3D lookup table is typically stored in cache memoryin a hardware implementation. Conventionally, the 3D lookup tables arealways symmetric such that the 3D lookup tables have a same size for theluma component, the first chroma component and the second chromacomponent. In addition, conventionally, the 3D lookup tables are alwaysbalanced such that a size of each dimension of the 3D lookup tables isalways the same. This results in large table sizes with highcomputational complexity and high signaling costs. For example, tablesizes may be up to 9×9×9 or 17×17×17.

In some cases, the size of the 3D lookup table used for color gamutscalability is too large, which may lead to difficulty in practicalimplementations. In addition, the large table size and the use oftri-linear interpolation for the 3D lookup table results in highcomputational complexity.

In U.S. patent application Ser. No. 14/512,177, filed Oct. 10, 2014, thefollowing methods are proposed so that both signaling cost andcomputational complexity for the 3D lookup table based color gamutscalability may be reduced.

The first method includes generating an asymmetric 3D lookup table suchthat the luma (Y) and chroma (U and V) components have different sizes.In some cases, the 3D lookup table may have a larger size, i.e., moresegments or octants, for the luma component than for each of the firstand second chroma components. In this case, the chroma components mayuse a coarser lookup table and the luma component may use a more refinedlookup table. For example, table sizes may be up to 8×2×2. In othercases, the 3D lookup table may have a larger size for one or both of thechroma components than for the luma component.

The second method includes generating an unbalanced 3D lookup table,i.e. table[M][N][K], such that the size of each dimension is differentdepending on which color component is being used as a table index forthe 3D lookup table. The 3D lookup table may have a larger size for thedimension associated with the color component used as the table index.In this case, the color mapping may be more accurate for the colorcomponent used as the table index, while being less accurate for theother color components.

The third method includes generating only a luma component 3D lookuptable, and only using the 3D lookup table to perform luma componentprediction. The one-dimensional (1D) linear mapping or piecewise linearmapping techniques may be used for the chroma components.

The techniques of this disclosure are directed toward signaling of theinformation used to generate 3D lookup tables for color gamutscalability. According to the techniques, video encoder 20 may encodepartition information and/or color values of a 3D lookup table generatedfor color gamut scalability. Video decoder 30 may decode the partitioninformation and/or color values to generate the 3D lookup table in orderto perform color gamut scalability. The disclosed techniques provideefficient partitioning of the color components of the 3D lookup tableand efficient signaling of the partition information and/or color valuesfor the 3D lookup table. In this way, the disclosed techniques mayreduce both signaling cost and computational complexity for generatingthe 3D lookup table. The techniques described in this disclosure may beparticularly useful in signaling the information used to generateasymmetric and/or unbalanced 3D lookup tables.

In one example, the techniques described in this disclosure may providemore efficient partitioning of the color components of the 3D lookuptable by enabling asymmetric partitions such that the 3D lookup tablehas coarser partitioning for first and second chroma (e.g., Cb and Cr orU and V) components and finer partitioning for a luma (e.g., Y)component. The techniques may also provide more efficient signaling ofthe partition information for the 3D lookup table by signaling a numberof additional partitions for the luma component on top of a base numberof partitions for the 3D lookup table. In another example, thetechniques may provide more efficient partitioning of the colorcomponents of the 3D lookup table by enabling joint partitioning of thefirst and second chroma (e.g., Cb and Cr or U and V) components.

The techniques may also provide more efficient signaling of theinformation used to generate the 3D lookup table for color gamutscalability (CGS) by enabling one or more of the following. In a firstexample, a flag or an index may be signaled to indicate where the CGScolor prediction information is signaled, such as in a video parameterset (VPS), a sequence parameter set (SPS), a picture parameter set(PPS), a slice header or any other high level syntax header. In a secondexample, a number of partitions may be signaled to indicate a size,i.e., a number of segments or octants, of an asymmetric and/orunbalanced 3D lookup table. In a third example, when the chromacomponents are jointly partitioned, a range of a chroma center partitionmay be signaled.

In a fourth example, lower level (e.g., slice level) parameters of theCGS color prediction information may be predictively coded from higherlevel (e.g., PPS level) parameters of the CGS color predictioninformation. In a fifth example, a syntax table of the CGS colorprediction information may be signaled in the bitstream, such as in theVPS, SPS, PPS, or slice header. When several CGS color prediction syntaxtables are signaled at different locations in the bitstream, the syntaxtable at the lowest level that covers the picture to be coded may beused for the picture. In a sixth example, the syntax table of CGS colorprediction information may be conditionally signaled according towhether texture prediction is enabled for the picture to be coded. Whena higher layer of video data, i.e., an enhancement layer, has multipletexture reference layers, CGS color prediction syntax tables may besignaled for all or some of the reference layers whose color gamut isdifferent than the enhancement layer. In a seventh example, in order tomaintain low complexity, the CGS color prediction syntax table may befurther constrained to be signaled, at most, for only one referencelayer per picture.

In an eighth example, a partitioning boundary may be signaled for atleast one of the first and second chroma components in order to obtainuneven partitioning along the one of the chroma directions in the 3Dlookup table. The partitioning boundary information may be conditionallysignaled when the at least one of the chroma components is partitionedinto two or more segments or octants along the chroma direction.

Once each of the color components of the 3D lookup table is partitionedinto one or more octants, the techniques described in this disclosuremay provide more efficient signaling of the color values of the 3Dlookup table. The techniques include signaling, for each octant for eachof the color components of the 3D lookup table, either values ofvertexes of each of the octants or color mapping coefficients of alinear color mapping function for each of the octants. In thisdisclosure, the terms “partition,” “octant,” “segment,” and “cuboid,”may be used interchangeably to describe the partitioned regions of thecolor components of the 3D lookup table.

In a first example, for each octant for each of the color components,vertexes of the octant may be signaled. In this example, a residualvalue between a predicted value of a given vertex and an actual value ofthe given vertex may be signaled. In some cases, the residual value maybe further quantized. The quantization step information, e.g., aquantization value, may signaled or may be a predefined value. Theresidual value may be coded with kth-order exp-golomb coding. The orderk may be signaled in the bitstream or adaptively derived based on otherinformation, such as the magnitude of the residual values, in thebitstream. For each octant or partition, not all vertexes need to besignaled. For example, at least four vertexes may be signaled ifneighboring octants or cuboids do not share vertex values. The at leastfour vertexes may be used to interpolate all the values in the octant orcuboid.

In a second example, for each octant for each of the color components,color mapping coefficients (i.e., a, b, c and d) for a linear colormapping function of color values in the 3D lookup table may be signaledinstead of the vertexes of the octant. The linear color mapping functionwith color mapping parameters may be used directly to perform colorgamut prediction. The linear color mapping function is used to convertcolor data in a first color gamut for a lower layer of video data to asecond color gamut for a higher layer of video data, and the colormapping coefficients are weighting factors between color components ofthe lower and higher layers of the video data. In this disclosure, theterms “color mapping coefficients” and “linear color predictioncoefficients” may be used interchangeably. In addition, the terms“linear color mapping function,” “linear color prediction function,” and“3D linear equation,” may also be used interchangeably.

In this example, the color mapping coefficients (i.e., a, b, c and d)may be converted or quantized from floating point values to integervalues using a predefined number of bits. In some cases, the conversionor quantization information may be signaled in the bitstream. In othercases, the conversion or quantization information (i.e., the number ofbits used to represent the value of 1) may be dependent on at least oneof the input bit-depth or output bit-depth of the 3D lookup table.

For each of the color components, one of the color mapping coefficientsof the linear color mapping function may be a key coefficient thatdefines a weighting factor of the same color component being predicted.For example, when predicting the first chroma component of the higherlayer (i.e., U_(e)) using the linear color mapping functionU_(e)=a·Y_(b)+b·U_(b)+c·V_(b)+d, b is the key coefficient because it isthe weighting factor between the first chroma component of the lowerlayer (i.e., U_(b)) and the first chroma component of the higher layer(i.e., U_(e)) being predicted. The signaling of the key coefficient maybe different from the other coefficients. In some examples, theprediction of the key coefficients may be dependent on a predefinednon-zero value, while the prediction of the other coefficients may bedependent on a predicted value equal to zero. In other examples, theprediction of the key coefficients may be dependent on at least one ofthe input bit-depth or the output bit-depth of the 3D lookup table.

The numerous examples described above of techniques for efficientpartitioning and signaling a 3D lookup table for color gamut scalabilitymay be used alone or in any combination, and should not be limited tothe example combinations described in this disclosure. Additionaldetails of the disclosed techniques for efficient partitioning of thecolor components of the 3D lookup table and efficient signaling of thepartition information and/or color values for the 3D lookup table areprovided below.

As described above, in one example, video encoder 20 and/or videodecoder 30 may generate a 3D lookup table for color gamut scalability byperforming joint partitioning of the first and second chroma components.In a conventional 3D lookup table, the luma, first chroma, and secondchroma (i.e., Y, U, and V) components are independently partitioned.When each component is split into N segments or octants, the totalnumber of octants may be N×N×N, which results in a large 3D lookuptable. For example, table sizes may be up to 9×9×9 or 17×17×17. Toreduce the number of octants, the techniques of this disclosure mayprovide for independent partitioning of the luma (i.e., Y) componentwhile jointly partitioning the first and second chroma (i.e., U and V)components.

For example, the luma component may be evenly split into M partitions oroctants. The 2D U×V space of the first and second chroma components maythen be split into two partitions as follows:if (2^(CBit-1) −R<u<2^(CBit-1) +R and 2^(CBit-1) −R<v<2^(CBit-1)+R)(u,v)→Partition 0else(u,v)→Partition 1where (u, v) indicates the pixel values of the U and V components, CBitrepresents the bit depth of the chroma components, 2^(CBit-1)corresponds to a center value of the chroma pixels, and R denotes thedistance to the center value 2^(CBit-1). In some cases, R may be apredefined fixed value; otherwise R may be a value signaled in thebitstream, such as in the VPS, SPS, PPS, or slice header.

FIG. 13 is a conceptual illustration showing an example 3D lookup table158 with an independently partitioned luma component and jointlypartitioned chroma components. In the illustrated example of FIG. 13,the luma (i.e., Y) component is evenly partitioned into four partsaccording to partition lines 160A, 160B and 160C. The chroma (i.e., U-V)components are partitioned into two regions according to a partitioncuboid 162. In this case, for a chroma pair pixel value (u, v), it iseither inside partition cuboid 162 or outside partition cuboid 162. Inthe example of FIG. 13, 3D lookup table 158 is partitioned into 4×2=8partitions.

In another example, the chroma components (i.e., U-V) are jointlypartitioned while the luma component (i.e., Y) is split into Mpartitions, but the M partitions may not necessarily be the same size.In other words, the luma component may be unevenly partitioned such thatat least one of the partitions has a different size than the otherpartitions. For example, a partition located close to a center value ofthe luma component may be more refined, i.e., smaller, than thosepartitions located further away from the center value.

In the example of joint chroma component (i.e., U-V) partitioning, thesyntax tables and related semantics for signaling color mappingcoefficients of a linear color mapping function for color gamutscalability (CGS) may be as follows in Tables 1-3 below. Any edits,additions, or updates to the SHVC WD3, cited above, are indicated byitalicized text.

TABLE 1 Picture parameter set (PPS) RBSP syntax pic_parameter_set_rbsp() { Descriptor ...  pps_extension_flag u(1)  if( nuh_layer_id > 0 )  cgs_enable_flag u(1)  if( nuh_layer_id > 0 && cgs_enable_flag) {  cgs_info_in_pps_flag u(1)   if(cgs_info_in_pps_flag)   cgs_info_table( )  } ... }The cgs_enable_flag equal to 1 specifies that color gamut scalability isenabled. The cgs_enable_flag equal to 0 specifies that color gamutscalability is disabled. When not present, cgs_enable_flag is inferredto be 0.The cgs_info_in_pps_flag equal to 1 specifies that cgs_info_table ispresent in the PPS. cgs_info_in_pps_flag equal to 0 specifies thatcgs_info_table is not present in PPS but is present in slice header.When not present, cgs_info_in_pps_flag is inferred to be 0.

TABLE 2 Color gamut scalability (CGS) color prediction informationsyntax De- cgs_info_table( ) { scriptor  cgs_uv_part_range_from_centerue(v)  cgs_y_part_num_log2 ue(v)  for( i = 0; i < CGS_PART_NUM; i++ ) {  for( j = 0; j < 3 ; j++ ) {    for( l = 0; l < 4 ; l++ ) {     if ( j== l )      cgs_color_pred_coeff_minus128[i][j][l] se(v)     else     cgs_color_pred_coeff [i][j][l] se(v)    }   }  } }The cgs_uv_part_range_from_center syntax element specifies the range ofchroma partition from the center value of chroma component. When notpresent, cgs_uv_part_range_from_center is inferred to be 0.The cgs_y_part_num_log 2 syntax element specifies the number of lumapartitions in CGS color prediction. When not present, cgs_y_part_num_log2 is inferred to be 0. The CGS_PART_NUM parameter is derived as follows:CGS_PART_NUM=1<<(cgs_y_part_num_log 2+1).The cgs_color_pred_coeff_minus128 syntax element and thecgs_color_pred_coeff syntax element each specify color mappingcoefficients of a linear color mapping function for CGS. When notpresent, they are inferred to be 0. It should be noted that, in someexamples, the cgs_color_pred_coeff_minus128 and cgs_color_pred_coeffsyntax elements may be signaled using different entropy coding methods.In the example in Table 2 above, the entropy coding method of se(v) isused. Alternatively, kth-order exp-golomb coding or fixed length codingmay be used. It should also be noted that thecgs_color_pred_coeff_minus128 syntax element may indicate the predictedvalue for a key coefficient as a predefined fixed number equal to 128,which is the integer value used to represent a floating point value of1.0 in this example.

TABLE 3 Slice header syntax slice_segment_header( ) { Descriptor ...  if(nuh_layer_id > 0 && cgs_enable_flag && !cgs_info_in_pps &&NumActiveRefLayerPics > 0)    cgs_info_table( )   if(sample_adaptive_offset_enabled_flag ) { ... }When color gamut scalability is enabled (e.g., cgs_enable_flag=1) andthe cgs_info_table is not present in the PPS (e.g.,cgs_info_in_pps_flag=0), the cgs_info_table is not present in PPS but ispresent in the slice header.

As described above, in another example, video encoder 20 and/or videodecoder 30 may generate a 3D lookup table for color gamut scalabilitywith coarser partitioning for the first and second chroma (e.g., Cb andCr or U and V) components and finer partitioning for the luma (e.g., Y)component. Video encoder 20 and/or video decoder 30 may generate this 3Dlookup table by partitioning each of the color components into a numberof octants according to a base partition value, e.g., a maximal splitdepth for the 3D lookup table, and then further partitioning each of theoctants of the luma component based on a luma partition value. In oneexample, the luma partition value may be signaled in a bitstream byvideo encoder 20 to video decoder 30. In some cases, the base partitionvalue may also be signaled in the bitstream by video encoder 20 to videodecoder 30. In other cases, the luma partition value may be derived atboth video encoder 20 and video decoder 30, and/or the base partitionvalue may be a predefined value known at both the video encoder and thevideo decoder.

In one example, video encoder 20 and/or video decoder 30 firstconstructs the 3D lookup table in such a way that the each of the colorcomponents (i.e., the Y-U-V space) is iteratively and symmetricallysplit or partitioned until a predefined or signaled split depth isreached. The split depth defines a maximum number of times all of thecolor components of the 3D lookup table may be partitioned. In this way,the base partition value may be defined as a split depth. Then videoencoder 20 and/or video decoder 30 further evenly, or not evenly, splitseach smallest cube or octant along the luma (i.e., Y) direction so thatthe luma (i.e., Y) component has finer partitioning while the chroma(i.e., U and V) components have coarser partitioning.

For example, the proposed 3D lookup table with finer partitioning forthe luma component and coarser partitioning for the chroma componentsmay be signaled as follows in Table 4 below. Any edits, additions, orupdates to the SHVC WD3, cited above, are indicated by italicized text.

TABLE 4 3D lookup table color data syntax 3D_ LUT_ color_data ( ) {Descriptor  cur_octant_depth u(3)  cur_y_part_num_log2 u(2) input_bit_depth_minus8 u(4)  output_bit_depth_minus8 u(4) res_quant_bit u(3)  coding_octant( 0, 0, 0, 0, 1 << InputBitDepth) }The cur_octant_depth syntax element indicates the maximal split depthfor the Y-U-V space for the current table. In other words, thecur_octant_depth sytnax element indicates the base partition value forthe 3D lookup table.The cur_y_part_num_log 2 syntax element specifies the number of Ypartitions for the smallest cube. Alternatively, the cur_y_part_num_log2 syntax element specifies the number of Y partitions for the cube whosesplit_octant_flag is equal to 0. In other words, the cur_y_part_num_log2 syntax element indicates the luma partition value for the lumacomponent of the 3D lookup table. In one example, the base partitionvalue indicated by cur_octant_depth is equal to 1 such that each of thecolor components is partitioned into a single octant, and the lumapartition value indicated by cur_y_part_num_log 2 is equal to 4 suchthat the single octant of the luma component is partitioned into fouroctants, which results in a 3D lookup table of size 4×1×1. As anotherexample, the base partition value indicated by cur_octant_depth is equalto 2 such that each of the color components is partitioned into twooctants, and the luma partition value indicated by cur_y_part_num_log 2is equal to 4 such that each of the two octants of the luma component ispartitioned into four octants, which results in a 3D lookup table ofsize 8×2×2.The input_bit_depth_minus8 syntax element specifies the bit-depth of the3D lookup table entries. The InputBitDepth parameter may be computed asfollows: InputBitDepth=8+input_bit_depth_minus8.The ouput_bit_depth_minus8 syntax element specifies the bit-depth of the3D lookup table output. The OutputBitDepth parameter may be computed asfollows: OutputBitDepth=8+output_bit_depth_minus8.The res_quant_bit syntax element specifies the number of bits used inquantizing either vertex residual values or color mapping coefficientresidual values for each octant for each color component of the 3Dlookup table. The quantization of the residual values is achieved byright shifting the vertex residual values or the color mappingcoefficient residual values by res_quant_bit.

The coding_octant syntax table is described in more detail with respectto Table 5 below. In the example of the coding_octant syntax table shownin Table 5 below only the smallest octant or cuboid is further splitalong the luma (i.e., Y direction) such that the luma (i.e., Y)component has finer partitioning than the chroma (i.e., U and V)components. In some examples, any octant or cuboid may be split alongthe luma direction. In this example, whether an octant is further splitalong the luma direction may be signaled in the bitstream.

As described above, in a further example, video encoder 20 and/or videodecoder 30 may generate the 3D lookup table based on a number of octantsfor each of the color components and color values for each of theoctants. In some cases, the number of octants for at least one of thecolor components of the 3D lookup table may be signaled by video encoder20 to video decoder 30. In order for video decoder 30 to determine thecolor values for each octant for each of the color components of the 3Dlookup table, video encoder 20 may signal either vertexes of each of theoctants or color mapping coefficients for a linear color mappingfunction of color values for each of the octants.

In one example described above, for each of the octants or partitions,video encoder 20 may signal the color mapping coefficients of the linearcolor mapping function of the color values in the 3D lookup table. Thelinear color mapping function is used to convert color data in a firstcolor gamut for a lower layer of video data to a second color gamut fora higher layer of video data, and the color mapping coefficients areweighting factors between color components of the lower and higherlayers of the video data. For each of the color components, one of thecolor mapping coefficients may be a key coefficient that defines aweighting factor between the same color component of the lower andhigher layers of the video data.

The common linear color mapping function may be represented as follows.

$\begin{bmatrix}Y_{e} \\U_{e} \\V_{e}\end{bmatrix} = \begin{bmatrix}{{a_{00} \cdot Y_{b}} + {b_{01} \cdot U_{b}} + {c_{02} \cdot V_{b}} + d_{03}} \\{{a_{10} \cdot Y_{b}} + {b_{11} \cdot U_{b}} + {c_{12} \cdot V_{b}} + d_{13}} \\{{a_{20} \cdot Y_{b}} + {b_{21} \cdot U_{b}} + {c_{22} \cdot V_{b}} + d_{23}}\end{bmatrix}$In this example function, the subscript e and b denote the higher layer(i.e., enhancement layer) and lower layer (e.g., base layer),respectively, for each of the luma, first chroma, and second chromacolor components (i.e., Y, U, and V). The parameters a, b, c, and, drepresent the color mapping coefficients. In some examples, colormapping coefficients a₀₀, b₁₁ and c₂₂ represent the key coefficients foreach of the color components, i.e., the weighting factors between thesame color component of the base and enhancement layers). Although thesecoefficients are referred to as key coefficients in this disclosure,this name should not be considered limiting as similarly definedcoefficients may be referred to by other names. In some examples, thecolor mapping coefficients (i.e., a, b, c, and d) of the linear colormapping function for a given octant may be converted to the vertexes ofthe given octant first, and then the values of the vertexes may be codedin the bitstream to represent the color values in the 3D lookup table.

In some examples, the color mapping coefficients (i.e., a, b, c, and d)of the linear color mapping function are derived as floating pointvalues. In this example, video encoder 20 may convert or quantize thefloating point values of the color mapping coefficients into integervalues, and then encode the integer values into the bitstream for eachoctant. For example, the integer values of the color mappingcoefficients may be encoded in the cgs_info_table depicted in Table 2above, or may be encoded in the coding_octant table depicted in Table 5below. Video decoder 30 may then perform integer operations using theinteger values of the color mapping coefficients.

In order to represent the floating point values of the color mappingcoefficients with reasonable accuracy, an integer value is selected torepresent a floating point value of 1.0, e.g., using 256 (8 bits) as theinteger value to represent the floating point value of 1.0. Videoencoder 20 may perform the conversion or quantization according to thefollowing equation: A=└a·2^(N)┘, where a denotes the floating pointvalue of the color mapping coefficient to be converted or quantized, Ais the converted or quantized integer value, └x┘ indicates a floorfunction that rounds a parameter x to a maximal integer value that issmaller than x, and N indicates a number of bits needed to convert orquantize the floating point value of 1.0. In this way, the integervalues that represent the floating point values have a bit-depth (e.g.,8 bits) based on the parameter N.

In one example, the conversion or quantization may be based on theparameter N, in the exponent of the above equation A=└a·2^(N)┘, set to apredefined fixed value, such as 8 or 10. In another example, theconversion or quantization may be based on a value of N determined basedon at least one of an input bit-depth (i.e., B_(i)) or an outputbit-depth (i.e., B_(o)) of the 3D lookup table. For example, theconversion or quantization may be based on the parameter N determinedaccording to one of the following equations.N=B _(i),N=B _(o),N=10+B _(i) −B _(o), orN=8+B _(i) −B _(o).

In some examples, video encoder 20 and/or video decoder 30 may predictthe color mapping coefficients, and code residual values of the colormapping coefficients as the difference between original values of thecolor mapping coefficients and the predicted values of the color mappingcoefficients. For example, for a given octant, the prediction or part ofthe prediction for at least one of the color mapping coefficients, e.g.,one of the key coefficients, may be based on a predicted value equal toa predefined fixed value. In one example, the predicted value may be setequal to 2′, where N is the quantization bit value described above. Asanother example, for the given octant, the prediction or part of theprediction for at least one of the color mapping coefficients, e.g., oneof the key coefficients, may be dependent on at least one of the inputbit-depth (i.e., B_(i)) or the output bit-depth (i.e., B_(o)) of the 3Dlookup table. For example, the prediction or part of the prediction maybe based on a predicted value equal to 2^(N+B) ^(o) ^(−B) ^(i) .

As one example, video encoder 20 and/or video decoder 30 may performprediction of the color mapping coefficients as follows. For a firstoctant for each of the color components, the color mapping coefficientsof the linear color mapping function may be predicted based onpredefined fixed values. The key coefficient for each of the colorcomponents may be predicted differently than the other coefficients. Forexample, a key coefficient may be predicted based on a predicted valueequal to a predefined non-zero value, and any remaining color mappingcoefficients may be predicted based on a predicted value equal to zero.In this example, the color mapping coefficients of any remaining octantsfor each of the color components may be predicted based on predictedvalues from at least one previous octant, such as the first octant.

As another example of the prediction of the color mapping coefficients,for the first octant for each of the color components, the predictionvalue for the key coefficients for all the color components may be setequal to 2^(N+B) ^(o) ^(−B) ^(i) , and the prediction values for theother coefficients may be set equal to 0. In this example, thecoefficients of the remaining octants for each of the color componentsmay be predicted from the previous octant. In a further example, theprediction of the color mapping coefficients may be performed betweendifferent partitions or octants for each of the color components.Alternatively, a set of color mapping coefficients may be signaled asbase coefficients, such as in the SPS or PPS. Then, the differencesbetween the actual values of the color mapping coefficient and thevalues of the base coefficients may be signaled at the picture or slicelevel.

In some cases, the residual values of the color mapping coefficients maybe quantized based on a determined quantization value. Video encoder 20may signal the determined quantization value for video decoder 20 toperform inverse quantization to properly decode the color mappingcoefficients. In one example, the determined quantization value may beindicated by the res_quant_bit syntax element described in more detailwith respect to Table 4 above.

In this case, for each of the octants for each of the color components,video encoder 20 may calculate residual values of the color mappingcoefficients based on original values of the color mapping coefficientsand the predicted values of the color mapping coefficients, quantize theresidual values of the color mapping coefficients based on thedetermined quantization value, and then encode the residual values ofthe color mapping coefficients in the bitstream. Video encoder 20 mayalso encode the res_quant_bit syntax element to indicate the determinedquantization value. Video decoder 30 then decodes the res_quant_bitsyntax element and the residual values of the color mappingcoefficients, inverse quantizes the residual values of the color mappingcoefficients based on the determined quantization value, andreconstructs the color mapping coefficients based on the decodedresidual values and predicted values of the color mapping coefficients.

In addition, the values of the color mapping coefficients may berestricted to be within a given range based on a predefined fixed valueor a value dependent on at least one of an input bit-depth or an outputbit-depth of the 3D lookup table. The value of the color mappingcoefficients (i.e., a, b, c, and d) may be limited to a certain range toreduce the computational complexity of generating the 3D lookup table.As one example, the value can be restricted to be in the range of −2^(M)to 2^(M-1), inclusive, where M is set equal to a predefined fixed value,such as 10 or 12. Alternatively, the value of M may be dependent on oneor more of the quantization bit value N, the input bit-depth (i.e.,B_(i)) or the output bit-depth (i.e., B_(o)) of the 3D lookup table.

In another example described above, for each of the octants orpartitions, video encoder 20 may signal values of vertexes of the octantto indicate the color values in the 3D lookup table. The coding_octantsyntax table, which may be used to signal the color values of the 3Dlookup table, is primarily described in this disclosure with respect tosignaling values of octant vertexes. However, this description shouldnot be construed as limiting, as a substantially similar coding_octantsyntax table may be used to signal values of color mapping coefficientsfor a linear color mapping function for each octant.

The coding_octant syntax table, included in the 3D lookup table colordata syntax shown in Table 4 above, is described with respect to Table 5below. Any edits, additions, or updates to the SHVC WD3, cited above,are indicated by italicized text.

TABLE 5 Coding octant syntax coding_octant (depth, y,u,v,length) {Descriptor  if ( depth < cur octant depth )   split_octant_flag u(1)  if( split octant flag ) {    for( l = 0 ; l < 2 ; l++ )     for( m = 0 ; m< 2 ; m++ )      for( n = 0 ; n < 2 ; n++ )       coding_octant (depth+1, y+l*length/2, u+m*length/2,v+n*length/2, length/2)  }  else {  for( i = 0 ; i < YPartNum ; i++ )    for( vertex = 0 ; vertex < 4 ;vertex++ ) {     encoded_vertex_flag u(1)     if( encoded vertex flag ){      resY[yIdx][uIdx][vIdx][vertex] se(v)     resU[yIdx][uIdx][vIdx][vertex] se(v)     resV[yIdx][uIdx][vIdx][vertex] se(v)     }    }  } }The split_octant_flag equal to 1 specifies that an octant is split intoeight octants with half size in all directions for the purpose of vertexresidual octant coding. When not present, it is inferred to be equal to0.The variable YPartNum is derived as YPartNum=1<<cur_y_part_num_log 2.The encoded_vertex_flag equal to 1 specifies that the residuals of thevertex with index [yIdx2+i][uIdx][vIdx][vertex] are present. Theencoded_vertex_flag equal to 0 specifies that the residuals for thevertex are not present. When not present, the flag is inferred to beequal to zero.The variable yIdx is derived as follows.yIdx=(y+1*(length>>cur_y_part_num_log2))>>(InputBitDepth−cur_octant_depth−cur_y_part_num_log 2)The variable uIdx is derived as follows.uIdx=u>>(InputBitDepth−cur_octant_depth)The variable vIdx is derived as follows.vIdx=v>>(InputBitDepth−cur_octant_depth)resY[yIdx] [uIdx] [vIdx] [vertex], resU[yIdx] [uIdx] [vIdx] [vertex],andresV[yIdx][uIdx][vIdx][vertex] are the differences (i.e., residualvalues) between the Y, U, and V components of the vertex with index[yIdx][uIdx][vIdx][vertex] and the predicted Y, U, and V componentvalues for this vertex. When not present, these differencesresY[yIdx][uIdx][vIdx][vertex], resU[yIdx][uIdx][vIdx][vertex], andresV[yIdx][uIdx][vIdx][vertex] are inferred to be equal to 0.

In the example technique of signaling color mapping coefficients for alinear color mapping function for each octant of the 3D lookup table,the coding_octant syntax table may indicate residual values that are thedifferences between the color mapping coefficients (i.e., a, b, c, andd) for the linear color mapping function of the octant and the predictedcolor mapping coefficient values for the octant, instead of signalingthe vertex residual values resY[yIdx] [uIdx] [vIdx] [vertex], resU[yIdx][uIdx] [vIdx] [vertex], and resV[yIdx][uIdx][vIdx][vertex].

Returning to the example technique of signaling values of octantvertexes, each entry of the 3D lookup table may be derived as follows:lutX[yIdx][uIdx][vIdx][vertex]=(resX[yIdx][uIdx][vIdx][vertex]<<res_quant_bit)+predX[yIdx][uIdx][vIdx][vertex],where X indicates each of color components Y, U, and V, andpredX[yIdx][uIdx][vIdx][vertex] is derived according to Table 6 below.

TABLE 6 Predicted values for vertexes of octants in 3D lookup table[yIdx][uIdx][vIdx][vertex] vertex=0 vertex=1 vertex=2 vertex=3predY[yIdx][uIdx][vIdx][vertex] yIdx<<yoShift yIdx<<yoShiftyIdx<<yoShift (yIdx+1)<<yoShift predU[yIdx][uIdx][vIdx][vertex]uIdx<<uoShift (uIdx+1)<<uoShift (uIdx+1)<<uoShift (uIdx+1)<<uoShiftpredV[yIdx][uIdx][vIdx][vertex] vIdx<<voShift vIdx<<voShift(vIdx+1)<<voShift (vIdx+1)<<voShiftIn some cases, an additional offset may be applied during the shiftoperation of the prediction procedure described with respect to Table 6above.

In the example technique of signaling color mapping coefficients for alinear color mapping function for each octant of the 3D lookup table,similar equations may be used to derive or reconstruct the color mappingcoefficients (i.e., lutY, lutU, lutV) for the linear color mappingfunction of the 3D lookup table by inverse quantizing the residualvalues of the color mapping coefficients, and adding the inversequantized residual values of the color mapping coefficients to thepredicted values of the color mapping coefficients.

In some cases, the values of the color mapping coefficients lutY, lutUand lutV may be limited to a certain range to reduce the computationalcomplexity of generating the 3D lookup table. As one example, the valuecan be restricted to be in the range of −2^(M) to 2^(M-1), inclusive,where M is set equal to a predefined fixed value, such as 10 or 12.Alternatively, the value of M may be dependent on one or more of thequantization bit value N, the input bit-depth (i.e., B_(i)) or theoutput bit-depth (i.e., B_(o)) of the 3D lookup table.

After video encoder 20 and/or video decoder 30 generate the 3D lookuptable using one or more the example techniques described above, colorprediction may be performed as follows using the 3D lookup table. Theinput to the color prediction process is a (y,u,v) triplet in one colorspace, e.g., a first color gamut for a lower or base layer of videodata. The output of the color prediction process is a triplet (Y,U,V) inanother color space, e.g., a second color gamut for a higher orenhancement layer of video data. First, the smallest octant or cuboidthat covers the input triplet (y,u,v) is located in the 3D lookup table.Each of the indexes of the starting vertex of the cuboid are derived asfollows:yIndex=y>>(InputBitDepth−cur_octant_depth−cur_y_part_num_log 2)uIndex=u>>(InputBitDepth−cur_octant_depth)vIndex=v>>(InputBitDepth−cur_octant_depth)In some examples, an additional offset may be applied during the indexcalculation. Then, another three indexes of the octant or cuboid arederived as (yIndex, uIndex+1, vIndex); (yIndex, uIndex+1, vIndex+1); and(yIndex+1, uIndex+1, vIndex+1). These four vertexes may correspond tothe fourth case tetrahedral interpolation (P0, P1, P3, P7), which isillustrated as tetrahedron 156D in FIG. 12. The output triplet (Y,U,V)is then obtained by tetrahedral interpolation, which interpolates the 3Dlookup values of the four vertexes. In other examples, other cases oftetrahedral interpolation may be used. Alternatively, all eight vertexesof the octant or cuboid may be derived. In this case, tri-linearinterpolation may be used to derive the output triplet (Y, U, V).

In yet another example, a 3D lookup table may be signaled in the SPS orthe PPS. Then, in the slice header, an additional flag may be signaledto indicate whether the 3D lookup table will be overwritten for thecurrent slice. Alternatively or/and additionally, a 3D lookup table maybe signaled in the SPS and updated in the PPS. It should be noted thatcommon information, such as max_octant_depth, max_y_part_num_log 2,input_bit_depth, and output_bit_depth, may only be signaled at thehighest level, such as in the SPS or the PPS. Here max_octant_depth andmax_y_part_num_log 2 denote the maximum supported partition number ofthe 3D lookup table. In some cases, such information may be profileand/or level related instead of being signaled at the highest level.

As described above, in an additional example, video encoder 20 mayconditionally signal a partitioning boundary for at least one of thechroma components (i.e., U or V) of a 3D lookup table to video decoder30 based on the at least one of the chroma components being partitionedinto more than one octant, i.e., the base partition value being greaterthan one. In some cases, one or both of the chroma components may not beevenly partitioned. In other words, for a given one of the chromacomponents, at least one of the partitions has a different size than theother partitions. The partitioning boundary defines an unevenpartitioning of the one of the chroma components into two or moreoctants.

Conventionally, partition boundary information for each chroma componentis always signaled regardless of whether the chroma component is evenpartitioned into two or more segments or octants. According to thetechniques of this disclosure, in one example, video encoder 20 onlysignals the partitioning boundary when at least one of the chromacomponents (i.e., U or V) is partitioned into two or more parts.Otherwise, the partition boundary is unnecessary and is not signaled tothe video decoder. In another example, video encoder 20 only signals thepartitioning boundary when each of the chroma components (i.e., U and V)is partitioned into two or more parts.

In the example described with respect to Table 7 below, the condition isbased on the cur_octant_depth syntax element being equal to 1. Asdescribed above with respect to Table 4 above, the cur_octant_depthsyntax element indicates a base partition value as the maximal splitdepth for the 3D lookup table. When the cur_octant_depth syntax elementis equal to 1, each of the luma component, the first chroma component,and the second chroma component are partitioned into two segments oroctants. In this case, both of the chroma components (i.e., U and V)must be partitioned into two parts to satisfy the condition forsignaling partition boundary information. Any edits, additions, orupdates to the SHVC WD3, cited above, are indicated by italicized text.

TABLE 7 Color mapping table syntax colour_mapping_table( ) { Descriptor cm_input_luma_bit_depth_minus8 u(3)  cm_input_chroma_bit_depth_deltase(v)  cm_output_luma_bit_depth_minus8 u(3) cm_output_chroma_bit_depth_delta se(v)  if(cur octant depth==1) {  cb_part_threshold_minus_center se(v)   cr_part_threshold_minus_centerse(v)  }  colour_mapping_matrix( ) }The cb_part_threshold_minus_center syntax element specifies thepartition boundary for the first chroma (i.e., Cb) component. When thecb_part_threshold_minus_center syntax element is not present, it isinferred as 0.The variable CbPartThreshold is set equal to(1<<(cm_input_luma_bit_depth_minus8+cm_input_chroma_bit_depth_delta+7))+cb_part_threshold_minus_center.When a Cb value is smaller, or no larger, than the variableCbPartThreshold, the Cb value belongs to the first Cb partition.Otherwise, it belongs in the second Cb partition. Thecr_part_threshold_minus_center syntax element specifies the partitionboundary for the second chroma (i.e., Cr) component. When thecr_part_threshold_minus_center syntax element is not present, it isinferred as 0.The variable CrPartThreshold is set to(1<<(cm_input_luma_bit_depth_minus8+cm_input_chroma_bit_depth_delta+7))+cr_part_threshold_minus_center.When a Cr value is smaller, or no larger, than the variableCrPartThreshold, the Cr value belongs to the first Cr partition.Otherwise, it belongs in the second Cr partition. It should be notedthat the cb_part_threshold_minus_center andcr_part_threshold_minus_center syntax elements are not quantized priorto coding.

FIG. 14 is a block diagram illustrating an example of video encoder 20that may implement techniques for using 3D lookup table based colorgamut scalability in multi-layer video coding. Video encoder 20 mayperform intra- and inter-coding of video blocks within video slices.Intra-coding relies on spatial prediction to reduce or remove spatialredundancy in video within a given video frame or picture. Inter-codingrelies on temporal prediction to reduce or remove temporal redundancy invideo within adjacent frames or pictures of a video sequence. Intra-mode(I mode) may refer to any of several spatial based coding modes.Inter-modes, such as uni-directional prediction (P mode) orbi-prediction (B mode), may refer to any of several temporal-basedcoding modes.

As shown in FIG. 14, video encoder 20 receives a current video blockwithin a video frame to be encoded. In the example of FIG. 14, videoencoder 20 includes mode select unit 40, a video data memory 41, decodedpicture buffer 64, summer 50, transform processing unit 52, quantizationunit 54, and entropy encoding unit 56. Mode select unit 40, in turn,includes motion compensation unit 44, motion estimation unit 42,intra-prediction unit 46, partition unit 48, and color predictionprocessing unit 66. For video block reconstruction, video encoder 20also includes inverse quantization unit 58, inverse transform processingunit 60, and summer 62. A deblocking filter (not shown in FIG. 14) mayalso be included to filter block boundaries to remove blockinessartifacts from reconstructed video. If desired, the deblocking filterwould typically filter the output of summer 62. Additional filters (inloop or post loop) may also be used in addition to the deblockingfilter. Such filters are not shown for brevity, but if desired, mayfilter the output of summer 50 (as an in-loop filter).

Video data memory 41 may store video data to be encoded by thecomponents of video encoder 20. The video data stored in video datamemory 41 may be obtained, for example, from video source 18. Decodedpicture buffer 64 may be a reference picture memory that storesreference video data for use in encoding video data by video encoder 20,e.g., in intra- or inter-coding modes. Video data memory 41 and decodedpicture buffer 64 may be formed by any of a variety of memory devices,such as dynamic random access memory (DRAM), including synchronous DRAM(SDRAM), magnetoresistive RAM (MRAM), resistive RAM (RRAM), or othertypes of memory devices. Video data memory 41 and decoded picture buffer64 may be provided by the same memory device or separate memory devices.In various examples, video data memory 41 may be on-chip with othercomponents of video encoder 20, or off-chip relative to thosecomponents.

During the encoding process, video encoder 20 receives a video frame orslice to be coded. The frame or slice may be divided into multiple videoblocks. Motion estimation unit 42 and motion compensation unit 44perform inter-predictive coding of the received video block relative toone or more blocks in one or more reference frames to provide temporalprediction. Intra-prediction unit 46 may alternatively performintra-predictive coding of the received video block relative to one ormore neighboring blocks in the same frame or slice as the block to becoded to provide spatial prediction. Video encoder 20 may performmultiple coding passes, e.g., to select an appropriate coding mode foreach block of video data.

Moreover, partition unit 48 may partition blocks of video data intosub-blocks, based on evaluation of previous partitioning schemes inprevious coding passes. For example, partition unit 48 may initiallypartition a frame or slice into LCUs, and partition each of the LCUsinto sub-CUs based on rate-distortion analysis (e.g., rate-distortionoptimization). Mode select unit 40 may further produce a quadtree datastructure indicative of partitioning of an LCU into sub-CUs. Leaf-nodeCUs of the quadtree may include one or more PUs and one or more TUs.

Mode select unit 40 may select one of the coding modes, intra or inter,e.g., based on error results, and provides the resulting intra- orinter-coded block to summer 50 to generate residual block data and tosummer 62 to reconstruct the encoded block for use as a reference frame.Mode select unit 40 also provides syntax elements, such as motionvectors, intra-mode indicators, partition information, and other suchsyntax information, to entropy encoding unit 56.

Motion estimation unit 42 and motion compensation unit 44 may be highlyintegrated, but are illustrated separately for conceptual purposes.Motion estimation, performed by motion estimation unit 42, is theprocess of generating motion vectors, which estimate motion for videoblocks. A motion vector, for example, may indicate the displacement of aPU of a video block within a current video frame or picture relative toa predictive block within a reference picture (or other coded unit)relative to the current block being coded within the current picture (orother coded unit). A predictive block is a block that is found toclosely match the block to be coded, in terms of pixel difference, whichmay be determined by sum of absolute difference (SAD), sum of squaredifference (SSD), or other difference metrics. In some examples, videoencoder 20 may calculate values for sub-integer pixel positions ofreference pictures stored in decoded picture buffer 64. For example,video encoder 20 may interpolate values of one-quarter pixel positions,one-eighth pixel positions, or other fractional pixel positions of thereference picture. Therefore, motion estimation unit 42 may perform amotion search relative to the full pixel positions and fractional pixelpositions and output a motion vector with fractional pixel precision.

Motion estimation unit 42 calculates a motion vector for a PU of a videoblock in an inter-coded slice by comparing the position of the PU to theposition of a predictive block of a reference picture. The referencepicture may be selected from a first reference picture list (List 0) ora second reference picture list (List 1), each of which identify one ormore reference pictures stored in decoded picture buffer 64. Motionestimation unit 42 sends the calculated motion vector to entropyencoding unit 56 and motion compensation unit 44.

Motion compensation, performed by motion compensation unit 44, mayinvolve fetching or generating the predictive block based on the motionvector determined by motion estimation unit 42. Again, motion estimationunit 42 and motion compensation unit 44 may be functionally integrated,in some examples. Upon receiving the motion vector for the PU of thecurrent video block, motion compensation unit 44 may locate thepredictive block to which the motion vector points in one of thereference picture lists. Summer 50 forms a residual video block bysubtracting pixel values of the predictive block from the pixel valuesof the current video block being coded, forming pixel difference values,as discussed below. In general, motion estimation unit 42 performsmotion estimation relative to luma components, and motion compensationunit 44 uses motion vectors calculated based on the luma components forboth chroma components and luma components. Mode select unit 40 may alsogenerate syntax elements associated with the video blocks and the videoslice for use by video decoder 30 in decoding the video blocks of thevideo slice.

Intra-prediction unit 46 may intra-predict a current block, as analternative to the inter-prediction performed by motion estimation unit42 and motion compensation unit 44, as described above. In particular,intra-prediction unit 46 may determine an intra-prediction mode to useto encode a current block. In some examples, intra-prediction unit 46may encode a current block using various intra-prediction modes, e.g.,during separate encoding passes, and intra-prediction unit 46 (or modeselect unit 40, in some examples) may select an appropriateintra-prediction mode to use from the tested modes.

For example, intra-prediction unit 46 may calculate rate-distortionvalues using a rate-distortion analysis for the various testedintra-prediction modes, and select the intra-prediction mode having thebest rate-distortion characteristics among the tested modes.Rate-distortion analysis generally determines an amount of distortion(or error) between an encoded block and an original, unencoded blockthat was encoded to produce the encoded block, as well as a bit rate(that is, a number of bits) used to produce the encoded block.Intra-prediction unit 46 may calculate ratios from the distortions andrates for the various encoded blocks to determine which intra-predictionmode exhibits the best rate-distortion value for the block.

After selecting an intra-prediction mode for a block, intra-predictionunit 46 may provide information indicative of the selectedintra-prediction mode for the block to entropy encoding unit 56. Entropyencoding unit 56 may encode the information indicating the selectedintra-prediction mode. Video encoder 20 may include in the transmittedbitstream configuration data, which may include a plurality ofintra-prediction mode index tables and a plurality of modifiedintra-prediction mode index tables (also referred to as codeword mappingtables), definitions of encoding contexts for various blocks, andindications of a most probable intra-prediction mode, anintra-prediction mode index table, and a modified intra-prediction modeindex table to use for each of the contexts.

Video encoder 20 forms a residual video block by subtracting theprediction data from mode select unit 40 from the original video blockbeing coded. Summer 50 represents the component or components thatperform this subtraction operation. Transform processing unit 52 appliesa transform, such as a discrete cosine transform (DCT) or a conceptuallysimilar transform, to the residual block, producing a video blockcomprising residual transform coefficient values. Transform processingunit 52 may perform other transforms which are conceptually similar toDCT. Wavelet transforms, integer transforms, sub-band transforms orother types of transforms could also be used. In any case, transformprocessing unit 52 applies the transform to the residual block,producing a block of residual transform coefficients. The transform mayconvert the residual information from a pixel value domain to atransform domain, such as a frequency domain. Transform processing unit52 may send the resulting transform coefficients to quantization unit54.

Quantization unit 54 quantizes the transform coefficients to furtherreduce bit rate. The quantization process may reduce the bit depthassociated with some or all of the coefficients. The degree ofquantization may be modified by adjusting a quantization parameter. Insome examples, quantization unit 54 may then perform a scan of thematrix including the quantized transform coefficients. Alternatively,entropy encoding unit 56 may perform the scan.

Following quantization, entropy encoding unit 56 entropy codes thequantized transform coefficients. For example, entropy encoding unit 56may perform context adaptive variable length coding (CAVLC), contextadaptive binary arithmetic coding (CABAC), syntax-based context-adaptivebinary arithmetic coding (SBAC), probability interval partitioningentropy (PIPE) coding or another entropy coding technique. In the caseof context-based entropy coding, context may be based on neighboringblocks. Following the entropy coding by entropy encoding unit 56, theencoded bitstream may be transmitted to another device (e.g., videodecoder 30) or archived for later transmission or retrieval.

Inverse quantization unit 58 and inverse transform processing unit 60apply inverse quantization and inverse transformation, respectively, toreconstruct the residual block in the pixel domain, e.g., for later useas a reference block. Motion compensation unit 44 may calculate areference block by adding the residual block to a predictive block ofone of the frames of decoded picture buffer 64. Motion compensation unit44 may also apply one or more interpolation filters to the reconstructedresidual block to calculate sub-integer pixel values for use in motionestimation. Summer 62 adds the reconstructed residual block to themotion compensated prediction block produced by motion compensation unit44 to produce a reconstructed video block for storage in decoded picturebuffer 64. The reconstructed video block may be used by motionestimation unit 42 and motion compensation unit 44 as a reference blockto inter-code a block in a subsequent video frame.

According to the techniques described in this disclosure, video encoder20 is configured to perform 3D lookup table based color gamutscalability when encoding multi-layer video data. Video encoder 20 maypredict and encode multi-layer video data in accordance any of the SHVCextension, the MV-HEVC extension, and the 3D-HEVC extension, or othermulti-layer video coding extensions. Specifically, color predictionprocessing unit 66 of video encoder 20 may generate inter-layerreference pictures used to predict video blocks in a picture of a higherlayer of the video data when a color gamut for the higher layer of thevideo data is different than a color gamut for a lower layer of videodata.

Color prediction processing unit 66 of video encoder 20 may performcolor prediction using a 3D lookup table for color gamut scalability toconvert color data of a reference picture in a first color gamut for thelower layer of the video data to a second color gamut for the higherlayer of the video data. In some examples, color prediction processingunit 66 may generate a separate 3D lookup table for each of the colorcomponents, i.e., a luma component, a first chroma component and asecond chroma component. Each of the 3D lookup tables includes a lumadimension, a first chroma dimension and a second chroma dimension, andis indexed using the three independent color components.

The techniques of this disclosure relate to signaling of the informationused to generate 3D lookup tables for color gamut scalability. In someexamples of such techniques, video encoder 20 may encode partitioninformation and/or color values of a 3D lookup table generated for colorgamut scalability. The techniques described in this disclosure may beparticularly useful in signaling the information used to generateasymmetric and/or unbalanced 3D lookup tables.

In one example of the disclosed techniques, color prediction processingunit 66 of video encoder 20 may generate a 3D lookup table with coarserpartitioning for the first and second chroma components and finerpartitioning for the luma component. Color prediction processing unit 66may generate this 3D lookup table by partitioning each of the firstchroma, second chroma, and luma color components into a first number ofoctants according to a base partition value, e.g., a maximal split depthfor the 3D lookup table, and then further partitioning each of the firstnumber of octants of the luma component based on a luma partition value.In this way, each of the first and second chroma components of the 3Dlookup table are partitioned into fewer octants (i.e., coarserpartitioned) and the luma component of the 3D lookup table ispartitioned into more octants (i.e., finer partitioned).

As one example, the base partition value is equal to 1 such that each ofthe color components is partitioned into a single octant, and the lumapartition value is equal to 4 such that the single octant of the lumacomponent is partitioned into four octants, which results in a 3D lookuptable of size 4×1×1. As another example, the base partition value isequal to 2 such that each of the color components is partitioned intotwo octants, and the luma partition value is equal to 4 such that eachof the two octants of the luma component is partitioned into fouroctants, which results in a 3D lookup table of size 8×2×2. As can beseen, a lower partition value results in a coarser partitioning (i.e., asmaller number of octants) for a color component.

In some cases, color prediction processing unit 66 generates at leastone syntax element (e.g., a first syntax element) indicating the lumapartition value. In other cases, the luma partition value may be derivedor known at both video encoder 20 and video decoder 30. As one example,color prediction processing unit 66 may derive the luma partition valuebased at least in part on the base partition value. In some cases, colorprediction processing unit 66 may also generate at least one syntaxelement (e.g., a second syntax element) indicating the base partitionvalue. In other cases, the base partition value may be a predefinedvalue known at both video encoder 20 and video decoder 30. Entropyencoding unit 56 of video encoder 20 may then entropy encode the firstand/or second syntax element.

In addition, video encoder 20 may conditionally encode one or moresyntax elements indicating a partitioning boundary for at least one ofthe chroma components. The partitioning boundary defines an unevenpartitioning of the one of the chroma components into two or moreoctants. According to some examples of the techniques of thisdisclosure, video encoder 20 only encodes the syntax elements indicatingthe partitioning boundary when at least one of the chroma components ispartitioned into more than one octant, i.e., when the base partitionvalue is greater than one. Otherwise, signaling the partition boundaryis unnecessary.

In another example of the disclosed techniques, video encoder 20 maygenerate a 3D lookup table based on a number of octants for each of theluma, first chroma, and second chroma color components, and color valuesfor each of the octants. As described above, in some cases, videoencoder 20 may encode at least one syntax element indicating the numberof octants for at least one of the color components of the 3D lookuptable. Video encoder 20 may also encode the color values for each of theoctants for each of the color components. For example, video encoder 20may encode color mapping coefficients for a linear color mappingfunction of the color values in the 3D lookup table. The linear colormapping function is used to convert color data in the first color gamutfor the lower layer of video data to the second color gamut for thehigher layer of video data. The color mapping coefficients for thelinear color mapping function are weighting factors between colorcomponents of the lower and higher layers of the video data. For each ofthe color components, one of the color mapping coefficients may be a keycoefficient that defines a weighting factor between the same colorcomponent of the lower and higher layers of the video data.

The color mapping coefficients for the linear color mapping function maybe derived as floating point values. Prior to encoding the color mappingcoefficients, color prediction processing unit 66 of video encoder 20may convert the floating point values of the color mapping coefficientsto integer values. The conversion may use a bit-depth for the integervalues based on at least one of an input bit-depth or an outputbit-depth of the 3D lookup table. In addition, color predictionprocessing unit 66 may restrict the values of the color mappingcoefficients to be within a given range based on a predefined fixedvalue or a value dependent on at least one of an input bit-depth or anoutput bit-depth of the 3D lookup table.

In some examples of the techniques of this disclosure, color predictionprocessing unit 66 may predict one or more of the color mappingcoefficients in order to encode residual values between original valuesof the color mapping coefficients and the predicted values of the colormapping coefficients. For example, for a first octant for each of thecolor components, color prediction processing unit 66 may predict thecolor mapping coefficients of the linear color mapping function based onpredefined fixed values. In one example, for a first octant for each ofthe color components, color prediction processing unit 66 may encode akey coefficient of the linear color mapping function based on apredicted value equal to a predefined non-zero value, and encode anyremaining color mapping coefficients of the linear color mappingfunction based on a predicted value equal to zero. In this example,color prediction processing unit 66 may encode the color mappingcoefficients of any remaining octants for each of the color componentsbased on predicted values from at least one previously encoded octant,such as the first octant.

Entropy encoding unit 56 of video encoder 20 may then entropy encode theresidual values of the color mapping coefficients for the linear colormapping function for each of the octants for each of the colorcomponents. In some cases, prior to entropy encoding, video encoder 20may quantize the residual values of the color mapping coefficients usingquantization unit 54 based on a determined quantization value. Videoencoder 20 may encode the determined quantization value.

Upon generating the 3D lookup table, color prediction processing unit 66performs color prediction of a reference picture for the lower layer ofthe video data using the 3D lookup table, and generates at least oneinter-layer reference picture for the higher layer of the video databased on the color predicted reference picture. Upon generating theinter-layer reference picture, motion compensation unit 44 of videoencoder 20 may operate as described above to predict video blocks in apicture of the higher layer of the video data based on the inter-layerreference pictures generated using the 3D lookup table. Video encoder 20may then encode residual data of the video blocks in a bitstream fortransmission to video decoder 30.

FIG. 15 is a block diagram illustrating an example of video decoder 30that may implement techniques for determining using 3D lookup tablebased color gamut scalability in multi-layer video coding. In theexample of FIG. 15, video decoder 30 includes an entropy decoding unit70, a video data memory 71, motion compensation unit 72, intraprediction processing unit 74, color prediction processing unit 86,inverse quantization unit 76, inverse transform processing unit 78,decoded picture buffer 82 and summer 80. Video decoder 30 may, in someexamples, perform a decoding pass generally reciprocal to the encodingpass described with respect to video encoder 20 (FIG. 14). Motioncompensation unit 72 may generate prediction data based on motionvectors received from entropy decoding unit 70, while intra-predictionunit 74 may generate prediction data based on intra-prediction modeindicators received from entropy decoding unit 70.

Video data memory 71 may store video data, such as an encoded videobitstream, to be decoded by the components of video decoder 30. Thevideo data stored in video data memory 71 may be obtained, for example,from computer-readable medium 16, e.g., from a local video source, suchas a camera, via wired or wireless network communication of video data,or by accessing physical data storage media. Video data memory 71 mayform a coded picture buffer (CPB) that stores encoded video data from anencoded video bitstream. Decoded picture buffer 82 may be a referencepicture memory that stores reference video data for use in decodingvideo data by video decoder 30, e.g., in intra- or inter-coding modes.Video data memory 71 and decoded picture buffer 82 may be formed by anyof a variety of memory devices, such as dynamic random access memory(DRAM), including synchronous DRAM (SDRAM), magnetoresistive RAM (MRAM),resistive RAM (RRAM), or other types of memory devices. Video datamemory 71 and decoded picture buffer 82 may be provided by the samememory device or separate memory devices. In various examples, videodata memory 71 may be on-chip with other components of video decoder 30,or off-chip relative to those components.

During the decoding process, video decoder 30 receives an encoded videobitstream that represents video blocks of an encoded video slice andassociated syntax elements from video encoder 20. Entropy decoding unit70 of video decoder 30 entropy decodes the bitstream to generatequantized coefficients, motion vectors or intra-prediction modeindicators, and other syntax elements. Entropy decoding unit 70 forwardsthe motion vectors to and other syntax elements to motion compensationunit 72. Video decoder 30 may receive the syntax elements at the videoslice level and/or the video block level.

When the video slice is coded as an intra-coded (I) slice, intraprediction processing unit 74 may generate prediction data for a videoblock of the current video slice based on a signaled intra predictionmode and data from previously decoded blocks of the current frame orpicture. When the video frame is coded as an inter-coded (i.e., B or P)slice, motion compensation unit 72 produces predictive blocks for avideo block of the current video slice based on the motion vectors andother syntax elements received from entropy decoding unit 70. Thepredictive blocks may be produced from one of the reference pictureswithin one of the reference picture lists. Video decoder 30 mayconstruct the reference picture lists, List 0 and List 1, using defaultconstruction techniques based on reference pictures stored in decodedpicture buffer 82. Motion compensation unit 72 determines predictioninformation for a video block of the current video slice by parsing themotion vectors and other syntax elements, and uses the predictioninformation to produce the predictive blocks for the current video blockbeing decoded. For example, motion compensation unit 72 uses some of thereceived syntax elements to determine a prediction mode (e.g., intra- orinter-prediction) used to code the video blocks of the video slice, aninter-prediction slice type (e.g., B slice or P slice), constructioninformation for one or more of the reference picture lists for theslice, motion vectors for each inter-encoded video block of the slice,inter-prediction status for each inter-coded video block of the slice,and other information to decode the video blocks in the current videoslice.

Motion compensation unit 72 may also perform interpolation based oninterpolation filters. Motion compensation unit 72 may use interpolationfilters as used by video encoder 20 during encoding of the video blocksto calculate interpolated values for sub-integer pixels of referenceblocks. In this case, motion compensation unit 72 may determine theinterpolation filters used by video encoder 20 from the received syntaxelements and use the interpolation filters to produce predictive blocks.

Inverse quantization unit 76 inverse quantizes, i.e., de-quantizes, thequantized transform coefficients provided in the bitstream and decodedby entropy decoding unit 70. The inverse quantization process mayinclude use of a quantization parameter QP_(Y) calculated by videodecoder 30 for each video block in the video slice to determine a degreeof quantization and, likewise, a degree of inverse quantization thatshould be applied. Inverse transform processing unit 78 applies aninverse transform, e.g., an inverse DCT, an inverse integer transform,or a conceptually similar inverse transform process, to the transformcoefficients in order to produce residual blocks in the pixel domain.

After motion compensation unit 72 generates the predictive block for thecurrent video block based on the motion vectors and other syntaxelements, video decoder 30 forms a decoded video block by summing theresidual blocks from inverse transform processing unit 78 with thecorresponding predictive blocks generated by motion compensation unit72. Summer 80 represents the component or components that perform thissummation operation. If desired, a deblocking filter may also be appliedto filter the decoded blocks in order to remove blockiness artifacts.Other loop filters (either in the coding loop or after the coding loop)may also be used to smooth pixel transitions, or otherwise improve thevideo quality. The decoded video blocks in a given frame or picture arethen stored in decoded picture buffer 82, which stores referencepictures used for subsequent motion compensation. Decoded picture buffer82 also stores decoded video for later presentation on a display device,such as display device 32 of FIG. 1.

According to some examples of the techniques described in thisdisclosure, video decoder 30 is configured to perform 3D lookup tablebased color gamut scalability when decoding multi-layer video data.Video decoder 30 may decode and reconstruct predicted multi-layer videodata in accordance any of the SHVC extension, the MV-HEVC extension, the3D-HEVC extension, or other multi-layer video coding extensions to HEVC.Specifically, color prediction processing unit 86 of video decoder 30may generate inter-layer reference pictures used to predict video blocksin a picture of a higher layer of the video data when a color gamut forthe higher layer of the video data is different than a color gamut for alower layer of video data.

Color prediction processing unit 86 of video decoder 30 may performcolor prediction using a 3D lookup table for color gamut scalability toconvert color data of a reference picture in a first color gamut for thelower layer of the video data to a second color gamut for the higherlayer of the video data. In some examples, color prediction processingunit 86 may generate a separate 3D lookup table for each of the colorcomponents, i.e., a luma component, a first chroma component and asecond chroma component. Each of the 3D lookup tables includes a lumadimension, a first chroma dimension and a second chroma dimension, andis indexed using the three independent color components.

The techniques of this disclosure relate to signaling of the informationused to generate 3D lookup tables for color gamut scalability. Accordingto the techniques, video decoder 30 may decode partition informationand/or color values to generate a 3D lookup table in order to performcolor gamut scalability. The techniques described in this disclosure maybe particularly useful in signaling the information used to generateasymmetric and/or unbalanced 3D lookup tables.

In one example of the disclosed techniques, color prediction processingunit 86 of video decoder 30 may generate a 3D lookup table with coarserpartitioning for the first and second chroma components and finerpartitioning for the luma component. Color prediction processing unit 86may generate this 3D lookup table by partitioning each of the firstchroma, second chroma, and luma color components into a first number ofoctants according to a base partition value, e.g., a maximal split depthfor the 3D lookup table, and then further partitioning each of the firstnumber of octants of the luma component based on a luma partition value.In this way, each of the first and second chroma components of the 3Dlookup table are partitioned into fewer octants (i.e., coarserpartitioned) and the luma component of the 3D lookup table ispartitioned into more octants (i.e., finer partitioned).

As one example, the base partition value is equal to 1 such that each ofthe color components is partitioned into a single octant, and the lumapartition value is equal to 4 such that the single octant of the lumacomponent is partitioned into four octants, which results in a 3D lookuptable of size 4×1×1. As another example, the base partition value isequal to 2 such that each of the color components is partitioned intotwo octants, and the luma partition value is equal to 4 such that eachof the two octants of the luma component is partitioned into fouroctants, which results in a 3D lookup table of size 8×2×2. As can beseen, a lower partition value results in a coarser partitioning (i.e., asmaller number of octants) for a color component.

In some cases, entropy decoding unit 70 of video decoder 30 entropydecodes at least one syntax element (e.g., a first syntax element)indicating the luma partition value. In other cases, the luma partitionvalue may be derived or known at both video encoder 20 and video decoder30. As one example, color prediction processing unit 86 may derive theluma partition value based at least in part on the base partition value.In some cases, entropy decoding unit 70 may also decode at least onesyntax element (e.g., a second syntax element) indicating the basepartition value. In other cases, the base partition value may be apredefined value known at both video encoder 20 and video decoder 30.Color prediction processing unit 86 uses the predefined or signaled basepartition value and the derived or signaled luma partition value togenerate the 3D lookup table with coarser partitioning for the first andsecond chroma components and finer partitioning for the luma component,as described above.

In addition, video decoder 30 may conditionally decode one or moresyntax elements indicating a partitioning boundary for at least one ofthe chroma components. The partitioning boundary defines an unevenpartitioning of the one of the chroma components into two or moreoctants. According to the techniques of this disclosure, video decoder30 only decodes the syntax elements indicating the partitioning boundarywhen at least one of the chroma components is partitioned into more thanone octant, i.e., when the base partition value is greater than one.Otherwise, decoding the partition boundary is unnecessary.

In another example of the disclosed techniques, video decoder 30 maygenerate a 3D lookup table based on a number of octants for each of theluma, first chroma, and second chroma color components, and color valuesfor each of the octants. As described above, in some cases, videodecoder 30 may decode at least one syntax element indicating the numberof octants for at least one of the color components of the 3D lookuptable, or otherwise determine the number of octants for each of thecolor components of the 3D lookup table. Video decoder 30 may alsodecode the color values for each of the octants for each of the colorcomponents. For example, video decoder 30 may decode color mappingcoefficients for a linear color mapping function of the color values inthe 3D lookup table. The linear color mapping function is used toconvert color data in the first color gamut for the lower layer of videodata to the second color gamut for the higher layer of video data. Thecolor mapping coefficients for the linear color mapping function areweighting factors between color components of the lower and higherlayers of the video data. For each of the color components, one of thecolor mapping coefficients may be a key coefficient that defines aweighting factor between the same color component of the lower andhigher layers of the video data.

The color mapping coefficients for the linear color mapping function arefirst derived as floating point values. The floating point values arethen converted or quantized to integer values are signaled as integervalues. The conversion may use a bit-depth for the integer values basedon at least one of an input bit-depth or an output bit-depth of the 3Dlookup table. In addition, color prediction processing unit 86 mayrestrict the values of the color mapping coefficients to be within agiven range based on a predefined fixed value or a value dependent on atleast one of an input bit-depth or an output bit-depth of the 3D lookuptable.

Entropy decoding unit 70 of video decoder 30 may entropy decode residualvalues of the color mapping coefficients for the linear color mappingfunction for each of the octants for each of the color components. Insome cases, after entropy decoding and prior to reconstruction, videodecoder 30 may inverse quantize the residual values of the color mappingcoefficients using inverse quantization unit 76 based on a determinedquantization value. Video decoder 30 may decode a syntax elementindicating the determined quantization value.

According to the techniques of this disclosure, color predictionprocessing unit 86 may predict one or more of the color mappingcoefficients in order to reconstruct values of the color mappingcoefficients based on the residual values of the color mappingcoefficients and the predicted values of the color mapping coefficients.For example, for a first octant for each of the color components, colorprediction processing unit 86 may predict the color mapping coefficientsof the linear color mapping function based on predefined fixed values.In one example, for a first octant for each of the color components,color prediction processing unit 86 may decode a key coefficient of thelinear color mapping function based on a predicted value equal to apredefined non-zero value, and decode any remaining color mappingcoefficients of the linear color mapping function based on a predictedvalue equal to zero. In this example, color prediction processing unit86 may decode the color mapping coefficients of any remaining octantsfor each of the color components based on predicted values from at leastone previously decoded octant, such as the first octant.

Upon generating the 3D lookup table, color prediction processing unit 86performs color prediction of a reference picture for the lower layer ofthe video data using the 3D lookup table, and generates an inter-layerreference picture for the higher layer of the video data based on thecolor predicted reference picture. Upon generating the inter-layerreference pictures, motion compensation unit 72 of video decoder 30 mayoperate as described above to reconstruct video blocks in a picture ofthe higher layer of the video data based on decoded residual data andthe inter-layer reference pictures generated using the 3D lookup table.

FIG. 16 is a flowchart illustrating an example operation of encodingpartition information for at least one of the color components of a 3Dlookup table. The example operation of FIG. 16 is described herein asbeing performed by color prediction processing unit 66 of video encoder20 of FIG. 14. In other examples, the operation may be performed bycolor prediction processing unit 144 of FIG. 8.

According to the techniques of this disclosure, color predictionprocessing unit 66 of video encoder 20 may generate a 3D lookup tablewith coarser partitioning for the first and second chroma components andfiner partitioning for the luma component. Color prediction processingunit 66 may generate this 3D lookup table by partitioning each of theluma, first chroma, and second chroma components of the 3D lookup tableinto a first number of octants based on a base partition value (180). Inone example, the base partition value may be a maximal split depth forthe 3D lookup table. Color prediction processing unit 66 then furtherpartitions each of the first number octants of the luma component into asecond number of octants based on a luma partition value (182).

In some cases, video encoder 20 may encode at least one syntax element(e.g., a first syntax element) indicating the luma partition value forthe luma component of the 3D lookup table. In other cases, the lumapartition value may be derived or known at both video encoder 20 andvideo decoder 30. In some cases, video encoder 20 may also generate atleast one additional syntax element (e.g., a second syntax element)indicating the base partition value for the 3D lookup table. In othercases, the base partition value may be a predefined value known at bothvideo encoder 20 and video decoder 30.

In addition, video encoder 20 may conditionally encode one or moresyntax elements indicating a partitioning boundary for at least one ofthe chroma components. The partitioning boundary defines an unevenpartitioning of the one of the chroma components into two or moreoctants. According to the techniques of this disclosure, video encoder20 encodes the syntax elements indicating the partitioning boundary forat least one of the chroma components based on the one of the chromacomponents being partitioned into more than one octant, i.e., the basepartition value being greater than one.

Video encoder 20 may also encode color values for each of the octantsfor each of the color components. For example, video encoder 20 mayencode color values of vertexes for each of the octants of each of thecolor components. As another example, video encoder 20 may encode colormapping coefficients for a linear color mapping function of the colorvalues in the 3D lookup table. In this way, a video decoder, such asvideo decoder 30 from FIG. 15, may generate a 3D lookup table based onthe signaled partition information and signaled color values in order toperform color gamut scalability to decode multi-layer video data.

FIG. 17 is a flowchart illustrating an example operation of decodingpartition information for at least one of the color components of a 3Dlookup table. The example operation of FIG. 17 is described herein asbeing performed by color prediction processing unit 86 of video decoder30 of FIG. 15. In other examples, the operation may be performed bycolor prediction processing unit 144 of FIG. 8.

According to the techniques of this disclosure, video decoder 30determines a base partition value for the 3D lookup table (186). In somecases, video decoder 30 may decode, from a received bitstream, at leastone syntax element (e.g., a second syntax element) indicating the basepartition value. In other cases, the base partition value may be apredefined value known at both video encoder 20 and video decoder 30.Video decoder 30 also determines a luma partition value for a lumacomponent of the 3D lookup table (188). In some cases video decoder 30may decode, from the received bitstream, at least one syntax element(e.g., a first syntax element) indicating the luma partition value. Inother cases, video decoder 30 may derive the luma partition value. Inone example, video decoder 30 may derive the luma partition value basedat least in part on the base partition value.

Color prediction processing unit 86 of video decoder 30 uses the basepartition value and the luma partition value to generate the 3D lookuptable with coarser partitioning for the first and second chromacomponents and finer partitioning for the luma component. Colorprediction processing unit 86 may generate this 3D lookup table bypartitioning each of the luma, first chroma, and second chromacomponents of the 3D lookup table into a first number of octants basedon the base partition value (190). In one example, the base partitionvalue may be a maximal split depth for the 3D lookup table. Colorprediction processing unit 86 then further partitions each of the firstnumber of octants of the luma component into a second number of octantsbased on a luma partition value (192). In this manner, the lumacomponent may be partitioned to have a greater number of octants thaneach of the chroma components.

In addition, video decoder 30 may conditionally decode one or moresyntax elements indicating a partitioning boundary for at least one ofthe chroma components. The partitioning boundary defines an unevenpartitioning of the one of the chroma components into two or moreoctants. According to the techniques of this disclosure, video decoder30 decodes the syntax elements indicating the partitioning boundary forat least one of the chroma components based on the one of the chromacomponents being partitioned into more than one octant, i.e., the basepartition value being greater than one.

Video decoder 30 may also decode color values for each of the octantsfor each of the color components. For example, video decoder 30 maydecode color values of vertexes for each of the octants of each of thecolor components. As another example, video decoder 30 may decode colormapping coefficients for a linear color mapping function of the colorvalues in the 3D lookup table. In this way, video decoder 30 maygenerate a 3D lookup table based on the signaled partition informationand signaled color values in order to perform color gamut scalability todecode multi-layer video data.

FIG. 18 is a flowchart illustrating an example operation of encodingcolor values for each of the octants for each of the color components ofa 3D lookup table. The example operation of FIG. 18 is described hereinas being performed by color prediction processing unit 66 of videoencoder 20 of FIG. 14. In other examples, the operation may be performedby color prediction processing unit 144 of FIG. 8.

According to the techniques of this disclosure, video encoder 20 maygenerate a 3D lookup table based on a number of octants for each of theluma, first chroma, and second chroma color components, and color valuesfor each of the octants (200). Video encoder 20 may encode the colorvalues for each of the octants for each of the color components. Morespecifically, for each of the octants for each of the color components,video encoder 20 may encode color mapping coefficients for a linearcolor mapping function of the color values in the 3D lookup table (202).

Prior to encoding the color mapping coefficients, color predictionprocessing unit 66 of video encoder 20 may convert floating point valuesof the color mapping coefficients to integer values using a bit-depthbased on at least one of an input bit-depth or an output bit-depth ofthe 3D lookup table. In addition, color prediction processing unit 66may restrict the values of the color mapping coefficients to be within agiven range based on a predefined fixed value or a value dependent on atleast one of an input bit-depth or an output bit-depth of the 3D lookuptable.

Color prediction processing unit 66 may predict one or more of the colormapping coefficients in order to encode residual values between originalvalues of the color mapping coefficients and the predicted values of thecolor mapping coefficients. For example, for a first octant for each ofthe color components, color prediction processing unit 66 may encode akey coefficient of the linear color mapping function based on apredicted value equal to a predefined non-zero value, and encode anyremaining color mapping coefficients of the linear color mappingfunction based on a predicted value equal to zero. In this example,color prediction processing unit 66 may encode the color mappingcoefficients of any remaining octants for each of the color componentsbased on predicted values from at least one previously encoded octant,such as the first octant. In some cases, prior to encoding the residualvalues of the color mapping coefficients, video encoder 20 may quantizethe residual values of the color mapping coefficients based on adetermined quantization value.

Video encoder 20 may also encode at least one syntax element indicatingthe number of octants for at least one of the color components of the 3Dlookup table. In this way, a video decoder, such as video decoder 30from FIG. 15, may generate a 3D lookup table based on the signaledpartition information and the signaled color values in order to performcolor gamut scalability to decode multi-layer video data.

FIG. 19 is a flowchart illustrating an example operation of decodingcolor values for each of the octants for each of the color components ofa 3D lookup table. The example operation of FIG. 19 is described hereinas being performed by color prediction processing unit 86 of videodecoder 30 of FIG. 15. In other examples, the operation may be performedby color prediction processing unit 144 of FIG. 8.

According to some examples of the techniques of this disclosure, videodecoder 30 determines a number of octants for each of the luma, firstchroma, and second chroma color components of the 3D lookup table (204).In some cases, video decoder 30 may decode, from a received bitstream,at least one syntax element indicating the number of octants for atleast one of the color components of the 3D lookup table. Video decoder30 also decodes color values for each of the octants for each of thecolor components. More specifically, for each of the octants for each ofthe color components, video decoder 30 may decode color mappingcoefficients for a linear color mapping function of the color values inthe 3D lookup table (206). Color prediction processing unit 86 of videodecoder 30 then generates the 3D lookup table based on the number ofoctants for each of the luma, first chroma, and second chroma colorcomponents, and the color values associated with the color mappingcoefficients for each of the octants (208). Video decoder 30 may use the3D lookup table to perform color gamut scalability to decode multi-layervideo data.

Video decoder 30 may receive residual values of the color mappingcoefficients for the linear color mapping function for each of theoctants for each of the color components. In some cases, after decodingthe residual values of the color mapping coefficients, video decoder 30may inverse quantize the residual values of the color mappingcoefficients based on a determined quantization value. Color predictionprocessing unit 86 may then predict one or more of the color mappingcoefficients in order to reconstruct values of the color mappingcoefficients based on the signaled residual values of the color mappingcoefficients and the predicted values of the color mapping coefficients.For example, for a first octant for each of the color components, colorprediction processing unit 86 may decode a key coefficient of the linearcolor mapping function based on a predicted value equal to a predefinednon-zero value, and decode any remaining color mapping coefficients ofthe linear color mapping function based on a predicted value equal tozero. In this example, color prediction processing unit 86 may decodethe color mapping coefficients of any remaining octants for each of thecolor components based on predicted values from at least one previouslydecoded octant, such as the first octant.

After decoding the color mapping coefficients, the color mappingcoefficients may be integer values that represent floating point valuesusing a bit-depth based on at least one of an input bit-depth or anoutput bit-depth of the 3D lookup table. Color prediction processingunit 86 may restrict the values of the color mapping coefficients to bewithin a given range based on a predefined fixed value or a valuedependent on at least one of an input bit-depth or an output bit-depthof the 3D lookup table.

Certain aspects of this disclosure have been described with respect toextensions of the HEVC standard for purposes of illustration. However,the techniques described in this disclosure may be useful for othervideo coding processes, including other standard or proprietary videocoding processes not yet developed.

A video coder, as described in this disclosure, may refer to a videoencoder or a video decoder. Similarly, a video coding unit may refer toa video encoder or a video decoder. Likewise, video coding may refer tovideo encoding or video decoding, as applicable.

It is to be recognized that depending on the example, certain acts orevents of any of the techniques described herein can be performed in adifferent sequence, may be added, merged, or left out altogether (e.g.,not all described acts or events are necessary for the practice of thetechniques). Moreover, in certain examples, acts or events may beperformed concurrently, e.g., through multi-threaded processing,interrupt processing, or multiple processors, rather than sequentially.

In one or more examples, the functions described may be implemented inhardware, software, firmware, or any combination thereof. If implementedin software, the functions may be stored on or transmitted over as oneor more instructions or code on a computer-readable medium and executedby a hardware-based processing unit. Computer-readable media may includecomputer-readable storage media, which corresponds to a tangible mediumsuch as data storage media, or communication media including any mediumthat facilitates transfer of a computer program from one place toanother, e.g., according to a communication protocol. In this manner,computer-readable media generally may correspond to (1) tangiblecomputer-readable storage media which is non-transitory or (2) acommunication medium such as a signal or carrier wave. Data storagemedia may be any available media that can be accessed by one or morecomputers or one or more processors to retrieve instructions, codeand/or data structures for implementation of the techniques described inthis disclosure. A computer program product may include acomputer-readable medium.

By way of example, and not limitation, such computer-readable storagemedia can comprise RAM, ROM, EEPROM, CD-ROM or other optical diskstorage, magnetic disk storage, or other magnetic storage devices, flashmemory, or any other medium that can be used to store desired programcode in the form of instructions or data structures and that can beaccessed by a computer. Also, any connection is properly termed acomputer-readable medium. For example, if instructions are transmittedfrom a website, server, or other remote source using a coaxial cable,fiber optic cable, twisted pair, digital subscriber line (DSL), orwireless technologies such as infrared, radio, and microwave, then thecoaxial cable, fiber optic cable, twisted pair, DSL, or wirelesstechnologies such as infrared, radio, and microwave are included in thedefinition of medium. It should be understood, however, thatcomputer-readable storage media and data storage media do not includeconnections, carrier waves, signals, or other transitory media, but areinstead directed to non-transitory, tangible storage media. Disk anddisc, as used herein, includes compact disc (CD), laser disc, opticaldisc, digital versatile disc (DVD), floppy disk and Blu-ray disc, wheredisks usually reproduce data magnetically, while discs reproduce dataoptically with lasers. Combinations of the above should also be includedwithin the scope of computer-readable media.

Instructions may be executed by one or more processors, such as one ormore digital signal processors (DSPs), general purpose microprocessors,application specific integrated circuits (ASICs), field programmablelogic arrays (FPGAs), or other equivalent integrated or discrete logiccircuitry. Accordingly, the term “processor,” as used herein may referto any of the foregoing structure or any other structure suitable forimplementation of the techniques described herein. In addition, in someaspects, the functionality described herein may be provided withindedicated hardware and/or software modules configured for encoding anddecoding, or incorporated in a combined codec. Also, the techniquescould be fully implemented in one or more circuits or logic elements.

The techniques of this disclosure may be implemented in a wide varietyof devices or apparatuses, including a wireless handset, an integratedcircuit (IC) or a set of ICs (e.g., a chip set). Various components,modules, or units are described in this disclosure to emphasizefunctional aspects of devices configured to perform the disclosedtechniques, but do not necessarily require realization by differenthardware units. Rather, as described above, various units may becombined in a codec hardware unit or provided by a collection ofinteroperative hardware units, including one or more processors asdescribed above, in conjunction with suitable software and/or firmware.

Various examples have been described. These and other examples arewithin the scope of the following claims.

What is claimed is:
 1. A method of decoding video data, the methodcomprising: determining a number of octants for each of three colorcomponents of a three-dimensional (3D) lookup table for color gamutscalability; for each of the octants for each of the color components,decoding color mapping coefficients for a linear color mapping functionof color values in the 3D lookup table used to convert color data in afirst color gamut for a lower layer of the video data to a second colorgamut for a higher layer of the video data, wherein decoding the colormapping coefficients comprises, for a first one of the octants for eachof the color components, decoding at least one coefficient of the colormapping coefficients based on a predicted value of the at least onecoefficient of the color mapping coefficients, and wherein the at leastone coefficient of the color mapping coefficients comprises a keycoefficient that defines a weighting factor for the linear color mappingfunction between a same color component of the lower layer of the videodata and the higher layer of the video data; generating the 3D lookuptable based on the number of octants for each of the color componentsand color values associated with the color mapping coefficients for eachof the octants; decoding residual data of video blocks of the videodata; and reconstructing the video blocks of the video data based on thedecoded residual data and at least one reference picture generated usingthe 3D lookup table.
 2. The method of claim 1, wherein the color mappingcoefficients comprise integer values that represent floating pointvalues using a bit-depth based on at least one of an input bit-depth oran output bit-depth of the 3D lookup table.
 3. The method of claim 1,wherein the predicted value of the at least one coefficient of the colormapping coefficients is a predefined fixed value.
 4. The method of claim1, wherein decoding the color mapping coefficients further comprises,for the first one of the octants for each of the color components,decoding the key coefficient based on a predicted value equal to apredefined non-zero value, and decoding remaining coefficients of thecolor mapping coefficients based on a predicted value equal to zero. 5.The method of claim 1, wherein decoding the color mapping coefficientsfurther comprises, for each remaining one of the octants for each of thecolor components, decoding the color mapping coefficients based onpredicted values from at least one previously decoded octant.
 6. Themethod of claim 1, further comprising determining a quantization valuefor residual values of the color mapping coefficients, wherein decodingthe color mapping coefficients further comprises: for each of theoctants for each of the color components, decoding residual values ofthe color mapping coefficients; inverse quantizing the residual valuesof the color mapping coefficients based on the determined quantizationvalue; and reconstructing the color mapping coefficients based on thedecoded residual values and predicted values of the color mappingcoefficients.
 7. The method of claim 6, wherein determining thequantization value for residual values of the color mapping coefficientscomprises decoding at least one syntax element indicating thequantization value.
 8. The method of claim 1, further comprisingrestricting values of the color mapping coefficients to a range based onone of a predefined fixed value or a value dependent on at least one ofan input bit-depth or an output bit-depth of the 3D lookup table.
 9. Themethod of claim 1, wherein determining the number of octants for each ofthe color components comprises decoding at least one syntax elementindicating the number of octants for at least one of the colorcomponents of the 3D lookup table.
 10. The method of claim 1, furthercomprising: performing color prediction using the 3D lookup table toconvert color data of a reference picture in the first color gamut forthe lower layer of the video data to the second color gamut for thehigher layer of the video data; generating at least one inter-layerreference picture for the higher layer of the video data based on theconverted color data; decoding residual data of video blocks; andreconstructing the video blocks in a picture of the higher layer of thevideo data based on the decoded residual data and the at least oneinter-layer reference picture generated using the 3D lookup table.
 11. Amethod of encoding video data, the method comprising: generating athree-dimensional (3D) lookup table for color gamut scalability based ona number of octants for each of three color components and color valuesfor each of the octants; for each of the octants for each of the colorcomponents, encoding color mapping coefficients for a linear colormapping function of the color values in the 3D lookup table used toconvert color data in a first color gamut for a lower layer of the videodata to a second color gamut for a higher layer of the video data,wherein encoding the color mapping coefficients comprises, for a firstone of the octants for each of the color components, encoding at leastone coefficient of the color mapping coefficients based on a predictedvalue of the at least one coefficient of the color mapping coefficients,and wherein the at least one coefficient of the color mappingcoefficients comprises a key coefficient that defines a weighting factorfor the linear color mapping function between a same color component ofthe lower layer of the video data and the higher layer of the videodata; predicting video blocks of the video data based on at least onereference picture generated using the 3D lookup table; and encodingresidual data of the video blocks in a bitstream.
 12. The method ofclaim 11, further comprising, prior to encoding the color mappingcoefficient, converting floating point values of the color mappingcoefficients to integer values using a bit-depth based on at least oneof an input bit-depth or an output bit-depth of the 3D lookup table. 13.The method of claim 11, wherein the predicted value of the at least onecoefficient of the color mapping coefficients is a predefined fixedvalue.
 14. The method of claim 11, wherein encoding the color mappingcoefficients further comprises, for the first one of the octants foreach of the color components, encoding the key coefficient based on apredicted value equal to a predefined non-zero value, and encodingremaining coefficients of the color mapping coefficients based on apredicted value equal to zero.
 15. The method of claim 11, whereinencoding the color mapping coefficients further comprises, for eachremaining one of the octants for each of the color components, encodingthe color mapping coefficients based on predicted values from at leastone previously encoded octant.
 16. The method of claim 11, furthercomprising determining a quantization value for residual values of thecolor mapping coefficients, wherein encoding the color mappingcoefficients further comprises: for each of the octants for each of thecolor components, calculating residual values of the color mappingcoefficients based on original values of the color mapping coefficientsand predicted values of the color mapping coefficients; quantizing theresidual values of the color mapping coefficients based on thedetermined quantization value; and encoding the residual values of thecolor mapping coefficients.
 17. The method of claim 16, furthercomprising encoding at least one syntax element indicating thedetermined quantization value for residual values of the color mappingcoefficients.
 18. The method of claim 11, further comprising restrictingvalues of the color mapping coefficients to a range based on one of apredefined fixed value or a value dependent on at least one of an inputbit-depth or an output bit-depth of the 3D lookup table.
 19. The methodof claim 11, further comprising encoding at least one syntax elementindicating the number of octants for at least one of the colorcomponents of the 3D lookup table.
 20. The method of claim 11, furthercomprising: performing color prediction using the 3D lookup table toconvert color data of a reference picture in the first color gamut forthe lower layer of the video data to the second color gamut for thehigher layer of the video data; generating at least one inter-layerreference picture for the higher layer of the video data based on theconverted color data; predicting video blocks in a picture of the higherlayer of the video data based on the at least one inter-layer referencepicture generated using the 3D lookup table; and encoding residual dataof the video blocks in a bitstream.
 21. A video decoding devicecomprising: a memory configured to store video data; and one or moreprocessors in communication with the memory and configured to: determinea number of octants for each of three color components of athree-dimensional (3D) lookup table for color gamut scalability of thevideo data, for each of the octants for each of the color components,decode color mapping coefficients for a linear color mapping function ofcolor values in the 3D lookup table used to convert color data in afirst color gamut for a lower layer of the video data to a second colorgamut for a higher layer of the video data, wherein the one or moreprocessors are configured to, for a first one of the octants for each ofthe color components, decode at least one coefficient of the colormapping coefficients based on a predicted value of the at least onecoefficient of the color mapping coefficients, and wherein the at leastone coefficient of the color mapping coefficients comprises a keycoefficient that defines a weighting factor for the linear color mappingfunction between a same color component of the lower layer of the videodata and the higher layer of the video data, generate the 3D lookuptable based on the number of octants for each of the color componentsand color values associated with the color mapping coefficients for eachof the octants, decode residual data of video blocks of the video data,and reconstruct the video blocks of the video data based on the decodedresidual data and at least one reference picture generated using the 3Dlookup table.
 22. The device of claim 21, wherein the color mappingcoefficients comprise integer values that represent floating pointvalues using a bit-depth based on at least one of an input bit-depth oran output bit-depth of the 3D lookup table.
 23. The device of claim 21,wherein the predicted value of the at least one coefficient of the colormapping coefficients is a predefined fixed value.
 24. The device ofclaim 21, wherein the one or more processors are configured to, for thefirst one of the octants for each of the color components, decode thekey coefficient based on a predicted value equal to a predefinednon-zero value, and decode remaining coefficients of the color mappingcoefficients based on a predicted value equal to zero.
 25. The device ofclaim 21, wherein the one or more processors are configured to, for eachremaining one of the octants for each of the color components, decodethe color mapping coefficients based on predicted values from at leastone previously decoded octant.
 26. The device of claim 21, wherein theone or more processors are configured to: determine a quantization valuefor residual values of the color mapping coefficients; for each of theoctants for each of the color components, decode residual values of thecolor mapping coefficients; inverse quantize the residual values of thecolor mapping coefficients based on the determined quantization value;and reconstruct the color mapping coefficients based on the decodedresidual values and predicted values of the color mapping coefficients.27. The device of claim 26, wherein, to determine the quantization valuefor residual values of the color mapping coefficients, the one or moreprocessors are configured to decode at least one syntax elementindicating the quantization value.
 28. The device of claim 21, whereinthe one or more processors are configured to restrict values of thecolor mapping coefficients to a range based on one of a predefined fixedvalue or a value dependent on at least one of an input bit-depth or anoutput bit-depth of the 3D lookup table.
 29. The device of claim 21,wherein, to determine the number of octants for each of the colorcomponents, the one or more processors are configured to decode at leastone syntax element indicating the number of octants for at least one ofthe color components of the 3D lookup table.
 30. The device of claim 21,wherein the one or more processors are configured to: perform colorprediction using the 3D lookup table to convert color data of areference picture in the first color gamut for the lower layer of thevideo data to the second color gamut for the higher layer of the videodata; generate at least one inter-layer reference picture for the higherlayer of the video data based on the converted color data; decoderesidual data of video blocks; and reconstruct the video blocks in apicture of the higher layer of the video data based on the decodedresidual data and the at least one inter-layer reference picturegenerated using the 3D lookup table.
 31. A video encoding devicecomprising: a memory configured to store video data; and one or moreprocessors in communication with the memory and configured to: generatea three-dimensional (3D) lookup table for color gamut scalability of thevideo data based on a number of octants for each of three colorcomponents and color values for each of the octants; and for each of theoctants for each of the color components, encode color mappingcoefficients for a linear color mapping function of the color values inthe 3D lookup table used to convert color data in a first color gamutfor a lower layer of the video data to a second color gamut for a higherlayer of the video data, wherein the one or more processors areconfigured to, for a first one of the octants for each of the colorcomponents, encode at least one coefficient of the color mappingcoefficients based on a predicted value of the at least one coefficientof the color mapping coefficients, and wherein the at least onecoefficient of the color mapping coefficients comprises a keycoefficient that defines a weighting factor for the linear color mappingfunction between a same color component of the lower layer of the videodata and the higher layer of the video data, predict video blocks of thevideo data based on at least one reference picture generated using the3D lookup table, and encode residual data of the video blocks in abitstream.
 32. The device of claim 31, wherein, prior to encoding thecolor mapping coefficients, the one or more processors are configured toconvert floating point values of the color mapping coefficients tointeger values using a bit-depth based on at least one of an inputbit-depth or an output bit-depth of the 3D lookup table.
 33. The deviceof claim 31, wherein the predicted value of the at least one coefficientof the color mapping coefficients is a predefined fixed value.
 34. Thedevice of claim 31, wherein the one or more processors are configuredto, for the first one of the octants for each of the color components,encode the key coefficient based on a predicted value equal to apredefined non-zero value, and encode remaining coefficients of thecolor mapping coefficients based on a predicted value equal to zero. 35.The device of claim 31, wherein the one or more processors areconfigured to, for each remaining one of the octants for each of thecolor components, encode the color mapping coefficients based onpredicted values from at least one previously encoded octant.
 36. Thedevice of claim 31, wherein the one or more processors are configuredto: determine a quantization value for residual values of the colormapping coefficients; for each of the octants for each of the colorcomponents, calculate residual values of the color mapping coefficientsbased on original values of the color mapping coefficients and predictedvalues of the color mapping coefficients; quantize the residual valuesof the color mapping coefficients based on the determined quantizationvalue; and encode the residual values of the color mapping coefficients.37. The device of claim 36, wherein the one or more processors areconfigured to encode at least one syntax element indicating thedetermined quantization value.
 38. The device of claim 31, wherein theone or more processors are configured to restrict values of the colormapping coefficients to a range based on one of a predefined fixed valueor a value dependent on at least one of an input bit-depth or an outputbit-depth of the 3D lookup table.
 39. The device of claim 31, whereinthe one or more processors are configured to encode at least one syntaxelement indicating the number of octants for at least one of the colorcomponents of the 3D lookup table.
 40. The device of claim 31, whereinthe one or more processors are configured to: perform color predictionusing the 3D lookup table to convert color data of a reference picturein the first color gamut for the lower layer of the video data to thesecond color gamut for the higher layer of the video data; generate atleast one inter-layer reference picture for the higher layer of thevideo data based on the converted color data; predict video blocks in apicture of the higher layer of the video data based on the at least oneinter-layer reference picture generated using the 3D lookup table; andencode residual data of the video blocks in a bitstream.
 41. A videodecoding device comprising: means for determining a number of octantsfor each of three color components of a three-dimensional (3D) lookuptable for color gamut scalability; means for decoding, for each of theoctants for each of the color components, color mapping coefficients fora linear color mapping function of color values in the 3D lookup tableused to convert color data in a first color gamut for a lower layer ofthe video data to a second color gamut for a higher layer of the videodata, wherein the means for decoding the color mapping coefficientscomprises means for decoding, for a first one of the octants for each ofthe color components, at least one coefficient of the color mappingcoefficients based on a predicted value of the at least one coefficientof the color mapping coefficients, and wherein the at least onecoefficient of the color mapping coefficients comprises a keycoefficient that defines a weighting factor for the linear color mappingfunction between a same color component of the lower layer of the videodata and the higher layer of the video data; means for generating the 3Dlookup table based on the number of octants for each of the colorcomponents and color values associated with the color mappingcoefficients for each of the octants; means for decoding residual dataof video blocks of the video data; and means for reconstructing thevideo blocks of the video data based on the decoded residual data and atleast one reference picture generated using the 3D lookup table.
 42. Anon-transitory computer-readable storage medium storing having storedthereon instructions that, when executed, cause one or more processorsto: determine a number of octants for each of three color components ofa three-dimensional (3D) lookup table for color gamut scalability; foreach of the octants for each of the color components, decode colormapping coefficients for a linear color mapping function of color valuesin the 3D lookup table used to convert color data in a first color gamutfor a lower layer of the video data to a second color gamut for a higherlayer of the video data, wherein the instructions that cause theprocessor to decode the color mapping coefficients comprise instructionsthat cause the processor to, for a first one of the octants for each ofthe color components, decode at least one coefficient of the colormapping coefficients based on a predicted value of the at least onecoefficient of the color mapping coefficients, and wherein the at leastone coefficient of the color mapping coefficients comprises a keycoefficient that defines a weighting factor for the linear color mappingfunction between a same color component of the lower layer of the videodata and the higher layer of the video data; generate the 3D lookuptable based on the number of octants for each of the color componentsand color values associated with the color mapping coefficients for eachof the octants; decode residual data of video blocks of the video data;and reconstruct the video blocks of the video data based on the decodedresidual data and at least one reference picture generated using the 3Dlookup table.